Beyond Milk Production: Circular Economy Opportunities in Dairy Waste Management

Pranav Patil, Bapurao Kadam, Deepali Sakunde, Tejas Shende, Shubham Pawar,

Rahul Galgunde, Onkar Shende, Paramsai Desai, Pradnya Patil, Priya Pathare

KNP College of Veterinary Science, Shirwal, Satara 412 801, Maharashtra Animal and Fishery Sciences University, Nagpur

Abstract

India is the world’s largest milk producer, and the dairy sector plays a vital role in rural livelihoods, nutritional security, and economic development. However, the rapid expansion of dairy farming and dairy processing industries has led to the generation of substantial quantities of waste, including cattle dung, urine, wastewater, whey, and other by-products. Improper disposal of these wastes can result in environmental pollution, greenhouse gas emissions, nutrient losses, and public health concerns. The circular economy approach offers a sustainable solution by transforming dairy waste into valuable resources, thereby promoting resource efficiency, environmental protection, and economic gains. This review highlights the major components of dairy waste and explores various waste-to-wealth strategies, including biogas and Bio-CNG production, organic manure and vermicompost generation, biofertilizers and biopesticides from cow urine, wastewater recycling, biomass and bioplastic production, and the development of value-added products such as bio-briquettes. The environmental and economic benefits of dairy waste utilization, including renewable energy generation, nutrient recycling, reduced pollution, enhanced soil fertility, and additional income opportunities for farmers, are discussed. The article also examines key government policies and initiatives supporting sustainable dairy waste management in India, such as GOBAR-Dhan, SATAT, AHIDF, and the National Bioenergy Programme. Furthermore, current challenges related to waste handling, infrastructure, technology adoption, and resource recovery are analyzed. Finally, emerging innovations in smart dairy farming, precision livestock systems, carbon credit mechanisms, integrated crop-livestock farming, advanced bioenergy technologies, and climate-smart dairy production are presented as future pathways for sustainable dairy waste management. Adoption of these circular economy practices can transform dairy waste from an environmental burden into a valuable resource, contributing to sustainable agriculture, rural development, renewable energy production, and climate resilience.

Keywords: Dairy waste, Circular economy, Biogas, Bio-CNG, Vermicompost, Biofertilizers, Waste-to-wealth, Sustainable dairy farming, Resource recovery, Climate-smart agriculture.

Introduction

              According to Kona et al., (2025), India is the world’s largest milk-producing country, and the dairy sector plays a crucial role in strengthening the rural economy, ensuring nutritional security, and generating livelihoods for millions of farmers. The transformation of India from a milk-deficit nation to a global dairy leader stands as one of the most remarkable achievements in agricultural development. In 1951, the country produced only 17 million tonnes of milk with a per capita availability of merely 130 g/day. Through strategic initiatives such as Operation Flood, cooperative movements, technological advancements, and the relentless efforts of dairy farmers, India achieved 75 million tonnes of milk production by 1998 and emerged as the world’s leading milk producer. This growth has continued steadily, and during 2024–25, India recorded an estimated milk production of 247.87 million tonnes with a per capita availability of 485 g/day, despite becoming the world’s most populous nation. Major milk-producing states such as Uttar Pradesh, Rajasthan, Madhya Pradesh, Gujarat, and Maharashtra together contribute more than half of the national milk output. At the same time, indigenous cattle, crossbred cattle, and buffaloes remain the primary contributors to production, according to data published by BAHS 2025, Govt. of India. These achievements highlight the resilience, adaptability, and potential of the Indian dairy sector. However, the rapid expansion of dairy farming has also increased the generation of dairy waste, including dung, urine, and wastewater, creating environmental and management challenges. In this context, the concept of a circular economy has gained significant importance, emphasising the principles of resource recycling, waste minimisation, and sustainable utilisation of by-products. A circular economy in dairy farming promotes the conversion of waste into valuable resources such as biogas for clean energy production, slurry and dung for organic manure and vermicompost, and urine for biofertilizers and bio-pesticides. These practices help reduce dependence on chemical fertilisers and fossil fuels while improving soil fertility, environmental health, and farm income. Furthermore, integrated waste management systems support climate-smart agriculture by lowering greenhouse gas emissions and promoting efficient resource utilisation. Thus, adopting waste-to-wealth approaches through circular economy practices not only enhances economic sustainability but also contributes to environmental protection and sustainable rural development, making it a vital pathway for the future of green dairy farming in India.

             The milk group contributes the largest share to the livestock sector economy in India and has shown remarkable growth over the years. The value of milk output increased steadily from ₹327,767 crore in 2011–12 to ₹1,116,241 crore in 2022–23, reflecting the rapid expansion and economic importance of the dairy industry. This substantial increase highlights rising milk production, improved dairy infrastructure, enhanced productivity, and growing consumer demand for milk and milk products. The continuous growth of the milk sector demonstrates its significant contribution to agricultural GDP, rural employment, and the overall development of the livestock economy in India, as data published under Value of output from Livestock Sector by National Accounts Statistics, MOSPI, GOI.

Concept of Circular Economy in Dairy Farming

             India’s agricultural sector is currently facing the combined challenge of increasing food production while maintaining the sustainability of natural resources required to support its population of over 1.4 billion people. Like every production system, agriculture and dairy farming generate significant amounts of waste throughout their production cycle. In the dairy sector, waste is produced at different stages of farm management and mainly includes solid and liquid wastes. Solid wastes consist of leftover feed, bedding materials, and animal dung, whereas liquid wastes include urine and water used for washing and cleaning purposes. Most dairy wastes are organic in nature and rich in carbon and essential nutrients, making them valuable resources for agricultural use. However, if not managed properly, these nutrient-rich wastes can lead to environmental problems such as nutrient leaching, greenhouse gas emissions, water contamination, and the spread of pathogens. Therefore, a proper understanding of waste generation, handling, and timely management is essential for efficient utilization of dairy waste. Effective waste management practices not only help in recycling nutrients and improving environmental sustainability but also reduce pollution and promote eco-friendly dairy farming systems, according to Bagrecha et al., (2025).

           The circular economy model in the dairy sector offers a sustainable approach to increasing farmers’ income while promoting efficient resource utilisation and environmental conservation. In dairy farming, cattle dung, which is often considered waste, can be converted into biogas and bio-fertilizers, reducing dependence on chemical fertilisers and fossil fuels while generating additional income for farmers through the sale of renewable energy and organic manure. Similarly, hides obtained from cattle that die naturally can be utilised for leather production, creating value-added products and preventing resource wastage. Beyond traditional dairy products such as milk, curd, and paneer, the sector also has significant potential to expand into speciality and value-added products for global markets, thereby improving the economic status of dairy farmers. To promote this circular economy approach, the Government of India has strengthened dairy cooperatives and introduced initiatives under White Revolution 2.0 to provide financial support, technology, and infrastructure for sustainable dairy practices. Successful examples such as Banas Dairy in Gujarat demonstrate how income generated from biogas and fertilisers can be shared directly with farmers. The dairy sector has also contributed significantly to women’s empowerment by ensuring direct income transfer systems and enhancing financial inclusion for women dairy farmers. The circular economy model creates additional revenue streams, reduces farm input costs through the use of biogas and biofertilizers, and promotes climate-smart and sustainable dairy farming systems. However, successful implementation requires investment in infrastructure such as biogas plants and fertiliser units, proper training and awareness among farmers, and strong market linkages for value-added products like leather and organic fertilisers. Therefore, with continuous government support, technological advancement, and farmer participation, the circular economy model can transform the Indian dairy sector into a more profitable, resilient, and environmentally sustainable system.

Overview of Dairy Waste Components and Their Composition

          Ahmad et al., (2019) stated that dairy product processing generates large quantities of waste and effluents, which are considered the major environmental concerns associated with the dairy industry. During the processing of milk and dairy products such as cheese, butter, yoghurt, cream, and milk powder, various solid and liquid wastes are produced. Solid wastes mainly include sludge, curd particles, spoiled milk, leftover feed, and butter or ghee sediment, while liquid wastes consist of processing water, cleaning wastewater, sanitary wastewater, whey, and milk residues lost during technological operations. Dairy wastewater is generally rich in organic matter, suspended solids, fats, oils, grease, lactose, proteins, nitrogen, phosphorus, and minerals, making it highly biodegradable but also environmentally hazardous if discharged untreated. In addition, residues of detergents, sanitisers, acids, and alkaline cleaning agents used for washing equipment and processing units further increase the pollution load of dairy effluents. Whey, the major by-product generated during cheese and casein production, contains valuable nutrients such as lactose, proteins, vitamins, minerals, and lipids, but is often wasted despite its economic potential. Dairy wastewater is characterised by high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), unpleasant odour, turbidity, and varying pH levels, indicating its strong pollution potential. Wastewater generation in dairy industries is significant, with approximately 6–10 litres of wastewater produced per litre of processed milk due to the extensive use of water during processing and cleaning operations. Sources of dairy waste include milk spillage, spoiled milk, whey permeates, starter cultures, cleaning-in-place (CIP) chemicals, washing of tanks, bottles, floors, and transportation equipment. Therefore, efficient management and treatment of dairy industrial waste are essential to reduce environmental pollution, recover valuable nutrients, and promote sustainable and circular dairy production systems.

          The rapidly increasing global demand for milk and dairy products has led to significant expansion and industrialisation of the dairy sector. The transition from traditional small-scale production systems to large-scale mechanised dairy processing has improved production capacity; however, it has also resulted in the generation of enormous quantities of dairy waste and effluents. Untreated dairy waste poses serious environmental concerns due to its high content of organic matter, nutrients, Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), oils, grease, detergents, acids, and alkaline cleaning agents, which can contaminate soil and water resources and negatively affect human and environmental health. Among the major by-products of the dairy industry, whey and buttermilk are considered highly significant because of their rich nutritional composition and industrial potential. Whey, the liquid remaining after casein removal during cheese and casein production, contains lactose, whey proteins, minerals, vitamins, and small amounts of fat, while buttermilk, obtained during butter production, contains valuable proteins, phospholipids, lactose, and milk fat. These by-products possess excellent functional and emulsifying properties and can be utilised in the preparation of beverages, bakery products, probiotics, bioactive compounds, microencapsulation materials, and fermented products. Recent advancements in biorefinery technologies, biotechnology, fermentation, and genetic engineering have further enhanced the utilisation of whey and buttermilk for producing value-added products such as biofuels, bioplastics, exopolysaccharides, microbial cultures, and functional foods. Fermentation of whey and buttermilk using beneficial microorganisms not only reduces environmental pollution but also contributes to the development of nutritionally enriched and commercially valuable products. Therefore, efficient utilisation of dairy by-products through innovative technologies supports the principles of the circular economy by reducing waste, recovering valuable nutrients, and promoting sustainable dairy processing systems, as reviewed by Hameed et al.,(2023).

Waste-to-Wealth Approaches in Dairy Farming

Biogas Production

         Biogas plays a crucial role as a renewable fuel in the decarbonization of the global economy due to its potential to replace fossil fuels while simultaneously managing organic waste streams. Raw biogas mainly consists of methane (CH4) and carbon dioxide (CO2), along with trace compounds such as ammonia, hydrogen sulfide, mercaptans, oxygen, and nitrogen. To improve its quality and usability, several upgrading and purification technologies are employed, including water scrubbing, pressure swing adsorption, membrane separation, chemical absorption, cryogenic separation, and biological CO2 fixation. These processes remove impurities and enrich methane concentration, enabling biogas to be used for electricity and heat generation, injected into natural gas grids, or utilised as a transport biofuel. Desulfurization methods such as iron salt addition, activated carbon adsorption, biological treatment, and micro-aeration are also commonly applied to reduce hydrogen sulfide levels and prevent corrosion problems in engines and pipelines. Compared with conventional biofuels such as bioethanol and biodiesel, biogas offers several advantages because it can be directly recovered from anaerobic digesters without requiring highly energy-intensive separation processes. It can be used independently or blended with diesel in compression ignition engines, significantly reducing particulate matter and NOx emissions. Furthermore, integrating anaerobic digestion with thermal technologies such as pyrolysis and gasification enhances resource recovery and energy efficiency. Pyrolysis-derived biochar can even serve as an adsorbent during biogas upgrading, lowering operational costs. However, the selection of upgrading technologies depends largely on plant scale, treatment capacity, and intended end use, as upgrading and compression substantially increase operational expenses.

         Despite its environmental benefits, the large-scale implementation of biogas technology still faces economic and social challenges. High capital investment, dependency on government subsidies, and public opposition to large waste treatment facilities limit widespread adoption in many countries. In Spain, for example, biogas contributes only a minor share of renewable electricity production compared to wind and hydropower, with most biogas originating from wastewater treatment plants and landfills. To improve the economic feasibility of anaerobic digestion, research has focused on increasing reactor productivity and biogas yield through thermal hydrolysis, ultrasonication, electrokinetic disintegration, and other pre-treatment technologies. Operating under thermophilic conditions and reducing hydraulic retention time can further enhance methane productivity while decreasing reactor volume. Ultimately, improving digestion efficiency, reducing upgrading and compression costs, and establishing supportive government policies are essential for biogas to become a major contributor to renewable energy systems and the decarbonization of the economy, as stated by Ellacuriaga et al. (2021).

         The promotion of biogas technology in India began on a large scale during 1981–1982 with the launch of the National Project on Biogas Development (NPBD) by the Ministry of Non-Conventional Energy Sources (MNES). The program aimed to popularise small-scale biogas plants suitable for households owning 2–4 livestock animals. To encourage adoption, the government provided substantial financial support for plant installation, technical assistance, and dissemination of biogas technology among rural communities. This initiative played a significant role in rural energy development at a time when conventional fuels such as liquefied petroleum gas (LPG) were not widely accessible in villages. As a result of the nationwide implementation of NPBD, biogas plants were established across several Indian states, with Maharashtra, Karnataka, Uttar Pradesh, Gujarat, and Madhya Pradesh emerging as the leading provinces in terms of installations. Maharashtra alone accounts for nearly one million small-scale biogas plants, while Madhya Pradesh has more than 376,000 installations, reflecting the widespread acceptance of biogas as a sustainable rural energy source. In India, small-scale biogas digesters are broadly categorised into two major types: floating-drum and fixed-dome biogas plants. Both systems operate as semicontinuous digesters and are designed to process livestock manure under anaerobic conditions to produce biogas. The floating drum type, commonly known as the KVIC model, generally ranges in size from 1–10 m3 and includes a floating gas holder, manure chamber, feed inlet, and effluent outlet. Variants of this design include KVIC, Pragati, Ganesh, and ferrocement floating drum models. In this system, the gas collector floats on the slurry surface and moves upward or downward depending on gas pressure and volume, thereby regulating gas supply. In contrast, fixed dome biogas plants have a permanently fixed gas chamber with a gas outlet at the top. These plants are usually constructed using concrete and include similar inlet and outlet arrangements as floating drum digesters. Comparative studies between the two designs indicate that fixed dome biogas plants are generally more economical and efficient than floating drum digesters. Floating drum systems experience relatively higher gas losses, especially when biogas is used to operate diesel engines, and their construction costs are almost double those of fixed dome plants. Moreover, floating drum digesters require greater technical expertise for operation and maintenance. These factors have contributed to the greater popularity of fixed-dome digesters in India and China. However, floating drum digesters possess the advantage of natural mixing and agitation due to the movement of the gas holder, which can slightly enhance biogas production. Despite these differences, detailed comparative studies evaluating the efficiency and productivity of various sizes of floating and fixed dome digesters are still limited. Overall, fixed dome digesters remain the most widely adopted small-scale biogas technology due to their lower cost, simpler design, and reduced gas losses, as reviewed by Pandey et al., (2021).

Organic manure & vermicompost production

            Vermicompost is a nutrient-rich organic fertiliser produced through the non-thermophilic biodegradation of organic matter by earthworms, a process known as vermicomposting. During this process, organic waste materials pass through the earthworms’ digestive system and are transformed into vermicast, a homogeneous, humus-like substance rich in essential plant nutrients and growth-promoting compounds. Vermicompost contains significant amounts of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), beneficial microorganisms, and humic substances that enhance soil fertility and plant growth. Its fine texture increases surface area, promoting microbial activity, nutrient retention, soil aeration, porosity, and water-holding capacity. Vermiculture has gained global attention as an effective and sustainable approach for organic waste management and soil fertility improvement. A wide range of organic wastes, including animal manure, municipal solid waste, crop residues, kitchen waste, paper industry sludge, dairy sludge, biogas slurry, aquatic weeds, invasive plant species, and industrial by-products, can be successfully converted into valuable vermicompost using earthworm species such as Eisenia fetida and Eudrilus eugeniae. Vermicomposting not only reduces waste volume but also lowers pathogen loads, decreases toxicity, immobilises heavy metals, and improves nutrient availability. Studies have demonstrated that vermicompost enhances soil microbial activity, nutrient cycling, soil aggregation, and organic matter content, contributing to sustainable agriculture and land restoration. Furthermore, its application has been shown to improve crop growth, yield, and quality in various crops, including tomato, pepper, maize, and French bean, while also suppressing certain soil-borne diseases. Due to these environmental and agronomic benefits, vermicomposting has emerged as a valuable technology for converting organic wastes into high-quality organic fertiliser and promoting sustainable agricultural production systems, according to Fernando et al.,(2021).

          A study conducted in the Ludhiana district of Punjab, India by Singh et al.,(2020), examined the organic waste management practices adopted by dairy farmers using an ex-post facto research design. A total of 80 dairy farmers were randomly selected and categorised into small and large dairy farming groups. The findings revealed that paddy straw was primarily used as animal bedding, although a considerable proportion of farmers still practised in situ burning of crop residues. Most farmers managed paddy stubble through mulching, while some continued to burn it in the fields. Wheat straw was universally utilised as livestock feed, and wheat stubble was predominantly managed through mulching. Regarding household waste management, the majority of farmers fed kitchen waste to livestock and converted garden and paper waste into farmyard manure. In terms of dairy waste management, all farmers prepared farmyard manure from cattle dung; however, livestock urine was generally discharged into drains, representing a loss of valuable nutrients and a potential environmental concern. Slightly more than half of the respondents utilised dairy waste for biogas production. Overall, most dairy farmers exhibited low organic waste utilisation scores. Statistical analysis indicated that social participation and farmers’ knowledge levels had a highly significant positive relationship (p < 0.01) with organic waste utilisation. These findings suggest that improving farmers’ awareness and technical knowledge is essential for promoting efficient and sustainable organic waste management practices.

          To improve organic waste utilisation in dairy farming, farmers should receive regular training on scientific waste management practices and be encouraged to adopt biogas and vermicomposting technologies through financial and technical support. Livestock urine can be utilised for preparing liquid organic fertilisers instead of being discarded, while crop residue burning should be replaced with sustainable practices such as mulching, composting, and residue incorporation. Strengthening extension services, farmer cooperatives, and awareness programs can enhance knowledge and adoption of these practices. Integrating waste recycling, biogas production, and nutrient recovery within a circular economy approach can improve farm profitability, soil health, and environmental sustainability.

Biofertilizers and Biopesticides from urine

           Rawat et al.,(2020) reviewed that Biopesticides are natural pest management products derived from biological sources such as plants, animals, microorganisms, and certain minerals. Unlike conventional chemical pesticides, biopesticides are biodegradable, environmentally friendly, target-specific, and generally less toxic to humans, animals, beneficial insects, and soil microorganisms. They are broadly classified into three categories: biochemical pesticides, microbial pesticides, and plant-incorporated protectants (PIPs). The use of biopesticides has increased significantly in recent years due to growing environmental concerns, increasing awareness of the adverse effects of synthetic pesticides, and rising consumer demand for organically produced food. Traditional farming systems have long utilised locally available biological resources for pest management, among which cow urine has emerged as one of the most valuable and versatile components.

          Cow urine possesses numerous agricultural and medicinal properties and has been extensively described in traditional Indian literature, including the Sushruta Samhita and Ashtanga Sangraha. Scientific studies have shown that cow urine contains approximately 95% water, 2.5% urea, and 2.5% minerals, salts, hormones, enzymes, amino acids, cytokines, and other bioactive compounds. Important constituents include nitrogen, phosphorus, potassium, calcium, iron, sulphur, carbonic acid, ammonia, uric acid, lactose, and growth-promoting substances. These compounds contribute to its antimicrobial, antifungal, insecticidal, and plant growth-promoting activities. Cow urine also enhances the activity of beneficial soil microorganisms, thereby improving soil fertility and nutrient cycling. Due to these properties, it is commonly used as an ingredient in traditional organic formulations such as Panchagavya, Jiwamrut, and Amrutpani, which serve as biofertilizers, biostimulants, and biopesticides. Several researchers have developed cow urine-based biopesticide formulations by combining it with medicinal and pesticidal plant extracts. One of the most widely used preparations is Panchagavya, which consists of cow dung, cow urine, milk, curd, ghee, sugarcane juice, tender coconut water, and ripe bananas. The ingredients are fermented under aerobic conditions for approximately ten days to promote microbial growth and the production of beneficial metabolites. The resulting product is diluted and applied as a foliar spray, where it acts as a plant growth promoter and disease suppressor. Studies have demonstrated that Panchagavya enhances crop growth, improves flowering and fruiting, increases yield, and strengthens plant resistance to pests and diseases. Neem (Azadirachta indica) is one of the most extensively studied plants used in combination with cow urine. Research has shown that aqueous neem leaf or neem seed kernel extracts mixed with cow urine exhibit strong insecticidal properties against a wide range of agricultural pests. Neem contains azadirachtin and related compounds that interfere with insect feeding, growth, and reproduction. When combined with cow urine, the effectiveness of neem-based formulations increases significantly due to synergistic effects. Gupta (2005) evaluated several combinations of neem leaf extract, neem kernel extract, and cow urine and reported effective control of crop pests following repeated field applications. Similarly, mixtures of cow urine and neem leaves soaked and fermented together have been found to possess excellent insecticidal, fungicidal, and plant growth-promoting properties without leaving harmful residues in the environment. Studies have also explored the efficacy of cow urine combined with other botanical extracts. Subedi and Vaidya (2003) reported that mixtures of cow urine with extracts of neem, Acorus calamus, Ageratum conyzoides, Urtica dioica, and other plants resulted in pest mortality exceeding 60%. Mohapatra et al. (2009) documented the successful use of various cow urine-based botanical formulations for controlling pests in rice, pulses, groundnut, and vegetable crops. Extracts of Vitex negundo, tulsi, lantana, jatropha, garlic, datura, eucalyptus, tobacco, agave, aloe vera, and calotropis, either alone or combined with cow urine, demonstrated significant pest suppression under field conditions. These formulations provide farmers with low-cost, locally available alternatives to synthetic pesticides.

          The combined use of cow urine and cow dung has also shown promising results in pest management. Boomathi et al., (2006) investigated different combinations of neem seed kernel extract, cow urine, and cow dung extract against Helicoverpa armigera, a major agricultural pest. The combination of neem seed kernel extract (5%), cow urine (5%), and cow dung extract (5%) produced insect mortality rates exceeding 80%, substantially higher than individual treatments. Likewise, studies on fruit borers revealed that alternate sprays of neem seed kernel extract and cow urine significantly reduced fruit damage and improved crop protection. Such combinations not only control pests effectively but also enrich the soil with beneficial microorganisms and nutrients. Beyond crop protection, cow urine-based biopesticides contribute to sustainable agriculture by improving soil health and promoting plant growth. Regular application stimulates microbial activity, enhances nutrient availability, and increases crop productivity. Fermented cow urine formulations are particularly beneficial because fermentation enhances microbial populations and reduces the risk of leaf scorching associated with fresh urine. Farmers generally dilute cow urine before application, with dilution ratios ranging from 1:1 to 1:4 depending on crop type and pest pressure. The use of fermented preparations also minimises phytotoxic effects while maximising pesticidal efficacy. Recent studies have extended the application of cow urine-based biopesticides beyond agriculture. Ashwini et al., (2014) demonstrated that formulations prepared from neem, Vitex negundo, and Parthenium hysterophorus extracts mixed with cow urine exhibited strong repellent activity against Aedes aegypti, the mosquito vector responsible for dengue and other viral diseases. Some formulations achieved repellency levels as high as 95%, highlighting the broader potential of botanical biopesticides in public health applications.

          Overall, cow urine-based biopesticides represent an effective, economical, and environmentally sustainable approach to pest management. Their ability to suppress pests and pathogens, enhance plant growth, improve soil fertility, and reduce dependence on synthetic chemicals makes them an important component of organic and natural farming systems. As concerns regarding pesticide residues, environmental pollution, and biodiversity loss continue to increase, the adoption of cow urine-based biopesticides offers a promising pathway toward sustainable and climate-resilient agriculture.

Wastewater recycling from dairy waste

         According to Ahmad et al.,(2019), Dairy industries generate large volumes of wastewater rich in organic matter, fats, proteins, nitrogen, and phosphorus, which can cause severe environmental pollution if discharged untreated into water bodies. Therefore, effective treatment and utilisation of dairy waste are essential for environmental protection and resource recovery. The major treatment approaches for dairy wastewater include wetland treatment, physico-chemical treatment, and biological treatment. Wetland treatment is considered a sustainable and eco-friendly method that utilises natural processes involving wetland plants, microorganisms, and substrate materials to remove pollutants from wastewater. Constructed wetlands offer several advantages over conventional treatment systems, including lower construction and operational costs, reduced energy requirements, simple maintenance, minimal sludge production, odour control, and improved air quality through carbon dioxide uptake by plants. These systems have been successfully used in several countries for dairy wastewater treatment and can achieve significant reductions in biochemical oxygen demand (BOD). However, wetlands require large land areas and may pose risks related to insect breeding and groundwater contamination if not properly managed. Physico-chemical treatment methods primarily focus on the removal of suspended solids, fats, proteins, and colloidal particles through processes such as coagulation and flocculation. Various natural and chemical coagulants, including chitosan, lactic acid bacteria, activated charcoal, iron salts, hydrogen peroxide, and tannin-based coagulants, have been used effectively to reduce chemical oxygen demand (COD), total dissolved solids, colour, odour, and turbidity in dairy wastewater. Natural coagulants such as tannins are particularly attractive because they are biodegradable, environmentally friendly, and effective across a broad pH range. These treatments serve as important pre-treatment steps that improve the efficiency of subsequent biological processes. Biological treatment is the most widely adopted method for dairy wastewater management due to its effectiveness in removing high organic loads.                                         

           Biological systems utilize microorganisms to degrade organic matter into simpler compounds. Depending on oxygen requirements, biological treatments are classified into aerobic and anaerobic processes. Aerobic treatments, such as activated sludge systems, aerated lagoons, trickling filters, and sequencing batch reactors (SBRs), operate in oxygen-rich environments and can achieve high removal efficiencies for COD, nitrogen, and organic pollutants. Advanced systems such as Intermittently Aerated Sequencing Batch Reactors (IASBR) have demonstrated nutrient removal efficiencies exceeding 90% while reducing energy consumption. Anaerobic treatment systems are particularly suitable for high-strength dairy wastewater because they are more cost-effective and generate valuable biogas as a by-product. Common anaerobic technologies include anaerobic digestion, Upflow Anaerobic Sludge Blanket (UASB) reactors, anaerobic filters, packed-bed bioreactors, and membrane anaerobic reactors. These systems can remove over 90% of COD while converting organic matter into methane-rich biogas, which can be used as a renewable energy source. Pretreatment techniques such as enzymatic hydrolysis using lipases further improve the degradation of fats and oils, enhancing reactor performance and preventing process failure due to lipid accumulation.

          In practice, a combination of aerobic and anaerobic treatments is often employed to achieve regulatory discharge standards. Anaerobic systems efficiently remove organic matter and generate energy, while aerobic processes provide additional polishing and nutrient removal. This integrated approach not only minimizes environmental pollution but also promotes resource recovery through biogas production, water reuse, and nutrient recycling. Therefore, sustainable dairy waste management should focus on combining efficient treatment technologies with waste valorisation strategies to convert dairy waste into valuable resources while protecting environmental and public health.

1. Biomass and Bioplastic production from dairy waste

          Dairy wastewater can be effectively utilised for biomass production while reducing environmental pollution. Studies have shown that the microalga Acutodesmus dimorphus can grow in raw dairy wastewater, removing over 90% of COD and completely utilising ammoniacal nitrogen within a few days. The resulting biomass contains significant amounts of lipids and carbohydrates, making it suitable for biodiesel and bioethanol production. Similarly, milk whey mixed with olive oil wastewater has been successfully used as a low-cost substrate for the growth of the fungus Geotrichum candidum, producing valuable microbial biomass without the need for additional nutrients. Thus, dairy wastewater can serve as an economical and sustainable resource for biomass and biofuel production while supporting wastewater treatment, as reviewed by Chokshi et al.,(2016).

          According to Pandian et al.,(2010), Dairy industry by-products, particularly whey, can be effectively utilised for the production of biodegradable bioplastics such as polyhydroxyalkanoates (PHAs), which are considered environmentally friendly alternatives to petroleum-based plastics. Several microorganisms can convert whey and whey-derived substrates into valuable bioplastics. For example, Ralstonia eutropha has been used to produce PHA from hydrolysed whey permeate, yielding polymers with desirable commercial properties. Similarly, Bacillus megaterium and Brevibacterium casei can utilise dairy waste as a carbon source for the production of polyhydroxybutyrate (PHB), the most common type of PHA. Other bacteria, such as Pseudomonas hydrogenovora, can also convert lactose-derived sugars into PHB. These biodegradable plastics offer significant environmental benefits by reducing plastic pollution and have important applications in packaging, agriculture, and medicine, including the production of nanoparticles for controlled drug delivery systems.

1. Value-added products from dairy wastes

          Bio-briquettes are solid renewable energy fuels produced by compressing biomass materials under pressure. High-quality briquettes are characterised by a smooth texture, good mechanical strength, easy ignition, long burning duration, low smoke emission, minimal soot production, and high calorific value. Traditionally, binders such as tapioca flour are used during briquette production; however, their use increases production costs, competes with food resources, and may generate additional smoke due to starch content. To overcome these limitations, researchers have explored the development of binder-free briquettes and the use of natural alternatives. Cow dung has emerged as a promising material because its natural fibrous content can act as a binding agent while also contributing energy value. Fresh cow dung contains carbon (29.35%), hydrogen (4.38%), oxygen (22.87%), nitrogen (1.85%), sulfur (0.37%), and has a calorific value of approximately 10.9 MJ/kg. When combined with coconut shell charcoal, which possesses a high calorific value of about 19.4 MJ/kg, high fixed carbon content, low ash content, and excellent fuel properties, the resulting bio-briquettes can serve as an efficient and environmentally friendly energy source. Coconut shell charcoal can also adsorb methane released from cow dung, helping to reduce greenhouse gas emissions while enhancing the calorific value of the briquettes. Therefore, the utilisation of cow dung and coconut shell charcoal for bio-briquette production represents a sustainable approach to waste management, renewable energy generation, and environmental protection, as studied by Sanchez et al., (2022).

         Biogas can be upgraded into Bio-CNG and used as a renewable substitute for compressed natural gas (CNG) in automobiles and transportation. A biogas scrubbing and bottling system developed at the Indian Institute of Technology Delhi utilises the principle of physical absorption, where carbon dioxide (CO₂), hydrogen sulfide (H₂S), and moisture are removed from raw biogas using pressurised water in a packed-bed scrubbing column operating under counter-current flow conditions. The purified methane-rich biogas is then compressed up to 20 MPa using a three-stage compressor, dried to remove residual moisture, and stored in high-pressure cylinders similar to those used for conventional CNG. Vehicle trials have demonstrated the suitability of the enriched biogas as a transportation fuel. This technology is particularly viable for large-scale biogas plants where sufficient quantities of biogas are available for purification and bottling, making Bio-CNG production economically feasible. The adoption of biogas enrichment and compression systems promotes sustainable waste utilisation, reduces dependence on fossil fuels, enhances rural energy security, generates employment opportunities, and supports environmental sustainability through the efficient use of cattle dung and other biomass resources studied by Vijay et al., (2006).

Environmental and economic benefits

          Effective utilisation of dairy waste offers significant environmental and economic advantages, contributing to sustainable livestock production and circular economy practices. Environmentally, the proper management of dairy waste reduces pollution of soil, water, and air by preventing the uncontrolled disposal of dung, urine, and wastewater. Conversion of dairy waste into products such as biogas, vermicompost, biofertilizers, biopesticides, bio-briquettes, and Bio-CNG helps reduce greenhouse gas emissions, particularly methane, while minimising dependence on chemical fertilisers and fossil fuels. Additionally, recycling nutrients through composting and vermicomposting improves soil fertility, enhances microbial activity, and promotes long-term soil health. From an economic perspective, dairy waste serves as a valuable resource that can generate additional income for farmers. Biogas and Bio-CNG production provide renewable energy for household, farm, and transportation purposes, reducing energy costs. Vermicompost and organic fertilisers can be used on-farm or sold commercially, while crop residues and dung can be converted into bio-briquettes and other value-added products. Improved nutrient recycling lowers expenditure on chemical fertilisers and waste disposal. Furthermore, dairy waste-based enterprises create employment opportunities in rural areas, support entrepreneurship, and enhance the overall profitability and sustainability of dairy farming systems. Thus, efficient dairy waste management transforms waste from an environmental liability into a valuable economic asset while supporting sustainable agricultural development.

Government policies and Initiatives about dairy waste management

          The Government of India has introduced several policies and initiatives to promote the scientific management and sustainable utilization of dairy waste, with the objectives of reducing environmental pollution, enhancing renewable energy production, and supporting circular economy practices in the livestock sector. The Central Pollution Control Board (CPCB) issued revised Guidelines for Environmental Management of Dairy Farms and Gaushalas in 2021, which provide recommendations for dung utilisation, solid waste management, wastewater treatment, air quality management, and siting of dairy farms. These guidelines promote sustainable practices such as composting and vermicomposting, biogas and compressed biogas (CBG) production, and the manufacture of dung-based fuel products. To strengthen waste-to-wealth initiatives, the Department of Animal Husbandry and Dairying implements the Animal Waste to Wealth Management component under the Animal Husbandry Infrastructure Development Fund (AHIDF), which offers interest subvention for establishing biogas, Bio-CNG, organic fertiliser, and cow dung/cow urine processing units. The GOBAR-Dhan scheme, launched under the Swachh Bharat Mission, encourages the conversion of cattle dung and agricultural residues into biogas, CBG, bio-slurry, and organic fertilisers, while the SATAT (Sustainable Alternative Towards Affordable Transportation) initiative promotes the production and marketing of compressed biogas as a renewable transport fuel. Additionally, the Ministry of New and Renewable Energy (MNRE) supports biogas generation through the National Bioenergy Programme (2021–26). Programs such as the National Mission on Sustainable Agriculture (NMSA) and Paramparagat Krishi Vikas Yojana (PKVY) further encourage composting, vermicomposting, organic farming, and nutrient recycling. The Rashtriya Gokul Mission and various state dairy development programs also support scientific manure management and value addition of cattle waste. Furthermore, the National Dairy Development Board (NDDB) has developed successful manure management models, including the Zakariyapura, Varanasi, and Banas models, which integrate biogas production, Bio-CNG generation, and organic fertilizer manufacturing. Through collaborations with dairy cooperatives across multiple states and dedicated financing schemes, NDDB is facilitating the large-scale adoption of sustainable dairy waste management practices. Collectively, these initiatives promote the transformation of dairy waste into renewable energy, organic fertilisers, biofertilizers, and other value-added products, thereby improving environmental quality, generating rural employment, enhancing farm income, and strengthening the sustainability of India’s dairy sector, according to an information bulletin published by the Ministry of Fisheries, Animal Husbandry & Dairying Govt. of India.

Current Challenges in Dairy Waste Handling and Resource Recovery

         Despite the immense potential of dairy waste as a source of renewable energy, organic fertilisers, and value-added products, its effective management remains a major challenge in many regions. One of the primary issues is the large volume of waste generated daily, including dung, urine, wastewater, and crop residues, which can lead to environmental pollution if not properly handled. Many dairy farmers, particularly smallholders, lack adequate infrastructure and financial resources for waste collection, storage, treatment, and processing. Limited awareness and technical knowledge regarding scientific waste management practices often result in inefficient utilisation or improper disposal of dairy waste. Open dumping of dung and discharge of wastewater can contaminate soil and water bodies, while improper handling of manure contributes to greenhouse gas emissions such as methane and nitrous oxide. The adoption of technologies such as biogas plants, vermicomposting units, and Bio-CNG production systems is often constrained by high initial investment costs, maintenance requirements, and limited access to technical support. In addition, dairy wastewater contains high levels of organic matter, fats, nitrogen, and phosphorus, making its treatment complex and costly. Seasonal fluctuations in waste availability, inadequate market linkages for organic products, and a lack of organised waste collection systems further hinder the commercialisation of dairy waste-based enterprises. Addressing these challenges requires improved farmer awareness, financial incentives, technological support, effective policies, and the development of integrated waste management systems that promote resource recovery and environmental sustainability.

Next-Generation Approaches to Sustainable Dairy Waste Management

          The future of dairy waste management is closely linked with the advancement of smart dairy farming, precision livestock systems, renewable bioenergy technologies, and climate-smart agricultural practices. Emerging smart dairy farms are increasingly adopting sensors, Internet of Things (IoT) devices, automated manure collection systems, and data-driven decision-making tools to monitor waste generation, optimise nutrient recycling, and improve overall farm efficiency. Precision livestock farming technologies enable real-time monitoring of animal health, feed utilisation, and manure production, allowing farmers to develop targeted waste management strategies that minimise resource losses and environmental impacts. Bioenergy technologies are expected to play a pivotal role in transforming dairy waste into valuable energy products. Advanced anaerobic digestion systems, biogas upgrading technologies, Bio-CNG production units, and biomass-based energy systems can convert cattle dung and dairy effluents into renewable fuels, electricity, and heat. Innovations in biorefinery approaches are also creating opportunities to produce high-value products such as biofertilizers, bioplastics, biochar, biopesticides, and industrial enzymes from dairy waste streams, thereby strengthening the circular bioeconomy.

         The growing emphasis on carbon neutrality and greenhouse gas mitigation has created new opportunities for dairy farmers through carbon credit and carbon trading mechanisms. Scientific manure management practices, methane capture from biogas plants, composting, vermicomposting, and nutrient recycling can significantly reduce greenhouse gas emissions, enabling farmers and dairy cooperatives to generate additional income through carbon credit markets. The integration of digital monitoring and verification systems will further facilitate participation in carbon offset programs. Integrated crop–livestock farming systems represent another promising approach for sustainable dairy waste utilisation. In such systems, livestock waste is recycled as organic manure, biofertilizer, or irrigation input for crop production, while crop residues are utilized as livestock feed, compost feedstock, or bioenergy substrates. This closed-loop nutrient cycle improves soil health, enhances resource-use efficiency, reduces external input requirements, and increases farm resilience. Climate-smart dairy production strategies are expected to prioritize low-emission livestock systems, efficient Milknutrient management, renewable energy adoption, and climate-resilient farming practices. Future innovations may include artificial intelligence-based waste management systems, automated nutrient recovery technologies, precision application of organic fertilizers, decentralized Bio-CNG plants, methane-reducing feed additives, and integrated waste-to-energy platforms. Collectively, these advancements will transform dairy waste from an environmental burden into a valuable resource, contributing to sustainable agriculture, enhanced farm profitability, improved environmental quality, rural employment generation, and long-term food and energy security.

Conclusions

         The dairy sector plays a pivotal role in India’s economy, food security, and rural livelihoods, contributing significantly to agricultural growth and employment generation. However, the rapid expansion of dairy farming and dairy processing industries has resulted in the generation of substantial quantities of solid and liquid wastes, including cattle dung, urine, wastewater, whey, and other by-products. If not managed properly, these wastes can contribute to environmental pollution, greenhouse gas emissions, nutrient losses, and public health concerns.

          The concept of a circular economy offers a sustainable framework for transforming dairy waste from an environmental liability into a valuable resource. Various waste-to-wealth approaches, such as biogas and Bio-CNG production, vermicomposting, organic manure preparation, biofertilizer and biopesticide development from cow urine, wastewater recycling, biomass generation, bioplastic production, and value-added products such as bio-briquettes, demonstrate the immense potential of dairy waste valorisation. These technologies not only reduce waste disposal problems but also promote renewable energy generation, nutrient recycling, soil health improvement, and diversification of farmers’ income sources.

         Government initiatives, including GOBAR-Dhan, SATAT, AHIDF, the National Bioenergy Programme, and NDDB-led manure management models, have further strengthened the adoption of sustainable dairy waste management practices across the country. Nevertheless, challenges such as inadequate infrastructure, limited technical knowledge, high investment costs, inefficient waste collection systems, and weak market linkages continue to hinder large-scale implementation.

          Future dairy waste management strategies should focus on integrating advanced technologies such as precision livestock farming, IoT-based monitoring systems, smart manure management, biorefineries, and climate-smart agricultural practices. Strengthening farmer awareness, policy support, financial incentives, and public-private partnerships will be essential for enhancing resource recovery and promoting widespread adoption of circular economy principles. Overall, sustainable dairy waste management represents a promising pathway toward environmental conservation, renewable energy production, improved farm profitability, rural development, and long-term sustainability of the dairy sector. By embracing waste-to-wealth approaches, the dairy industry can significantly contribute to achieving national goals related to climate resilience, resource efficiency, and sustainable agricultural development.

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