By the end of this chapter, you will be able to:
Mastering these skills helps you maintain a clean, safe, and efficient tannery environment, which is essential for protecting health and the environment in the trade.
The management of waste generated in tanneries is a critical aspect of sustainable leather production in Kenya. Tannery waste comprises various solid and liquid residues that can significantly impact the environment if not properly handled. Understanding the nature and composition of this waste, including key parameters such as total suspended solids, dissolved solids, and oxygen demand, is essential for effective segregation and treatment. This chapter equips leather technology professionals with the foundational knowledge to analyze and segregate tannery waste, ensuring compliance with environmental regulations and promoting eco-friendly practices within the leather industry.
Understanding key technical terms related to tannery waste is fundamental for professionals tasked with waste management. These terms define the physical and chemical characteristics of waste components and influence decisions on treatment and disposal methods within Kenyan tanneries.
Total Suspended Solids (TSS) refer to the particles suspended in water or wastewater that are not dissolved and can be trapped by filtration. In tannery effluents, TSS mainly comprise organic and inorganic matter such as hair, flesh particles, lime sludge, and undissolved tanning agents.
TSS in tannery wastewater originate from multiple processing stages including soaking, liming, fleshing, and tanning. These solids contribute to turbidity and can clog treatment systems if not removed early.
Elevated TSS levels increase the load on biological treatment systems by blocking light penetration and reducing oxygen transfer in aeration tanks. This can result in poor effluent quality and potential regulatory non-compliance.
TSS is commonly measured by filtering a known volume of wastewater through a standard filter, drying, and weighing the residue. This method provides a quantifiable indicator of particulate pollution.
Mechanical screening, sedimentation, and coagulation-flocculation are effective methods to reduce TSS before biological treatment. For example, at a leather processing plant in Nakuru, implementing sedimentation tanks reduced TSS by over 60%.
Dissolved Solids are substances dissolved in water, including salts, organic compounds, and minerals that pass through filters. They affect the chemical composition of tannery wastewater and influence treatment requirements.
Common dissolved solids include chlorides, sulfates, chromium salts, sodium, calcium, and organic matter from tanning chemicals. These components affect water hardness and conductivity.
High dissolved solids can increase the salinity of receiving waters, adversely affecting aquatic life. In treatment plants, they may cause scaling and corrosion in pipes and equipment.
Dissolved solids are often quantified by evaporating a filtered sample and measuring the residue or by using conductivity meters that estimate total dissolved solids (TDS) indirectly.
Ion exchange, reverse osmosis, and chemical precipitation are used to manage dissolved solids. For instance, a tannery in Eldoret adopted reverse osmosis to reduce chromium concentration in treated effluent.
Chemical Oxygen Demand (COD) quantifies the amount of oxygen required to chemically oxidize organic and inorganic matter in wastewater. It is a critical parameter indicating the pollution load of tannery effluents.
COD levels reflect the presence of oxidizable pollutants such as fats, oils, and tanning chemicals. High COD in tannery effluent signals heavy organic pollution that can deplete oxygen in receiving waters.
The standard method for COD determination involves digestion of a wastewater sample with a strong chemical oxidant under acidic conditions, followed by titration or instrumental analysis to measure oxygen equivalents.
COD provides a rapid estimate of pollution but does not differentiate between biodegradable and non-biodegradable substances. It is often used alongside BOD for comprehensive assessment.
Pretreatment processes like equalization, floatation, and chemical oxidation can reduce COD levels before biological treatment. For example, a leather factory in Kisumu implemented chemical coagulation to lower COD by 30%.
Biological Oxygen Demand (BOD) measures the amount of oxygen microorganisms consume to decompose organic matter in wastewater under aerobic conditions over a specified period, usually five days.
BOD indicates the biodegradable organic load and helps assess the effectiveness of biological treatment in tanneries. It is a key compliance parameter for discharge permits.
BOD testing involves incubating a sealed sample at 20°C for five days and measuring the oxygen consumed by microbes. This reflects the organic matter that can be biologically degraded.
Temperature, microbial activity, and the presence of toxic substances such as chromium can affect BOD measurements. Tannery effluent often shows high BOD due to organic residues.
High BOD requires robust biological treatment systems such as activated sludge or biofilters to prevent oxygen depletion in rivers and lakes. A SACCO-owned tannery in Meru upgraded its aeration system to handle elevated BOD loads.
Waste in the tannery context encompasses all unwanted materials generated during leather processing, including solid, liquid, and gaseous forms. Proper waste classification and segregation are essential for environmental protection and regulatory compliance.
Tannery waste includes solid wastes like trimmings, shavings, and sludge; liquid wastes such as spent tanning liquors and wastewater; and gaseous emissions including hydrogen sulfide from liming.
Improper disposal leads to soil contamination, water pollution, and health risks from toxic substances like chromium and sulfides. This necessitates stringent waste management practices.
Kenya's Environmental Management and Coordination Act (EMCA) regulates tannery waste disposal, requiring adherence to standards set by NEMA. Compliance safeguards community health and prevents fines.
Segregating waste at source into hazardous and non-hazardous streams facilitates appropriate treatment and recycling. For example, separating chrome-containing sludge from biodegradable waste enhances recovery of chromium.
Reducing waste generation through process optimization, chemical substitution, and recovery technologies contributes to sustainability. A Nairobi tannery introduced chemical recycling to reduce chromium sludge by 40%.
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Create a free accountThis chapter provided a comprehensive understanding of key terms related to tannery waste management, including total suspended solids, dissolved solids, chemical oxygen demand, biological oxygen demand, and waste itself. It explored the concept of pollution and its connection to tannery operations, emphasizing the role of sludge and effluent as byproducts requiring careful handling. The different types of waste generated in tanneries were examined, categorizing them into solid, liquid, and gaseous forms. The chapter highlighted the critical importance of waste treatment processes in mitigating environmental harm and discussed the negative effects that untreated waste can have on ecosystems and human health. Clean technology was introduced as an innovative approach to reducing pollution and improving waste management efficiency. Additionally, the sources and composition of tannery waste were analyzed to facilitate targeted management strategies. Finally, the chapter detailed methods for effective waste segregation and identified appropriate waste collection points to enhance overall waste handling within tannery settings.
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