Impact of Salinity and Resources Towards Adapting Greener Production for the Leather Industry

This study evaluated the environmental impact of hide and skin curing using marine salt in Kenya, focusing on how traditional leather preservation methods affect soil quality, wastewater contamination, and sustainability in the leather industry. Hide and skin curing is essential because it prevents decomposition, extends shelf life, and prepares raw materials for tanning. However, the process also creates serious environmental challenges due to the release of large amounts of salt and organic waste.

The research was conducted in Mariakani, a major leather-processing area in coastal Kenya, where wet salting is the most common preservation method. Although several techniques exist worldwide, including air-drying, frigorific drying, and suspension drying, wet salting accounts for nearly 85% of hide and skin curing in Kenya. Marine salt is widely used because of its availability, but it creates major pollution concerns. About 25–30% of the salt binds to the hide structure, while 70–75% remains on the surface and is later released as wastewater, airborne particles, or solid waste.

Kenya produces approximately 2.5 million hides and over 6 million skins annually, requiring between 9,300 and 13,000 tonnes of salt each year. This large-scale salt use creates major environmental risks, especially where waste management systems are weak. Blood, proteins, hair, fats, manure, and salt-rich wastewater accumulate and seep into surrounding land and water systems, making curing premises major pollution hotspots.

The study first examined blood yield after slaughter, which contributes significantly to effluent production. Sheep showed the highest blood yield percentage relative to body weight, producing 6.67% (±1.72), while cattle produced only 0.08% (±0.10). A sheep weighing 13 kg produced 0.87 litres of blood, while cattle weighing 330 kg yielded 2.84 litres. This shows that sheep contribute proportionally more to blood-rich effluent than cattle.

Moisture loss during wet salting was also measured on Day 7 and Day 14. Sheep skins showed the highest moisture loss, reaching about 8% by Day 14, while cattle hides and goat skins showed lower values. Coastal areas with high humidity (84%) and temperatures around 27°C showed different moisture loss patterns compared to cooler highland areas. Statistical analysis showed no significant difference for cattle hides and goat skins, but sheep skins showed significant variation, making them more sensitive to environmental conditions.

Wet salting also affected hide and skin size. Hides showed a 1.14% reduction in size between Day 1 and Day 7, while goatskins and sheepskins showed no major changes after Day 7. This suggests most shrinkage occurs early in the curing process.

Effluent analysis revealed extremely high pollution levels. Chemical Oxygen Demand (COD) reached 29,520 mg/L, showing severe organic pollution from blood, proteins, fats, and tissue residues. Turbidity reached 839.5 NTU, indicating high levels of suspended solids such as hair, debris, and decomposing matter. Particulate matter was also very high at 10 ppt.

The pH ranged from 5.5 to 6.4, showing moderate acidification of the wastewater. Salinity levels were extremely high, with electrical conductivity reaching 20 EC(ms) at the source and decreasing to 14.65 EC(ms) after lagoons. Excess sodium and chloride reduce soil fertility, prevent proper water absorption by plants, and create barren land.

Soil analysis showed severe damage in impacted areas compared to unimpacted zones. Beneficial bacteria, fungi, and actinomycetes were nearly absent in polluted soil, with only 2,180 viable cells per gram of dry soil compared to 54.7 million microbes per gram in unimpacted areas. Since soil microorganisms are essential for nutrient cycling and fertility, this indicates major biological degradation.

The polluted soil also showed high alkalinity (pH 8.18), excessive electrical conductivity (10 mS/cm), and nutrient imbalances in phosphorus, zinc, and potassium. High sodium content weakened soil structure, causing erosion and arid conditions. Salinity reduced both microbial life and physical soil stability, making the land unsuitable for farming or vegetation growth.

The study also noted that salt-rich effluent affects nearby buildings and infrastructure because airborne salt particles increase corrosion of roofs and structures. Plants also suffer from osmotic stress in saline soils, making survival difficult even with irrigation.

The research concluded that while wet salting is an effective preservation method, its environmental cost is very high when waste management is poor. It contributes to soil salinization, microbial depletion, wastewater contamination, and land degradation, threatening both ecosystems and the long-term sustainability of the leather industry.

The study recommended further investigation into land restoration and remediation. Sustainable alternatives such as low-salt curing methods, salt recovery systems, phytoremediation, and improved wastewater treatment should be prioritized. Stronger environmental regulations and occupational health standards are also necessary to support greener leather production and protect both the environment and future industrial productivity.