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Raw hides and skins are preserved before processing them into leather, to protect the skin protein from microbial attack. The salting method of preservation using about 50% w/w common salt is the most popularly practiced preservation method worldwide. This conventional system results in high saline wastewater leading to a huge amount of pollution load in terms of total dissolved solids and chlorides which is discharged into the effluent during the soaking process in leather manufacture. In order to overcome these wastes problem at their source, researchers have been involved in search of alternative preservation methods using salt-less or less-salt options. In the present study, the herbal Rumex abyssinicus (mekmeko) roots, which were shade dried at room temperature and powdered was investigated for its effectiveness in the preservation of goat skins. The efficacy of this new preservation method was assessed at different curing period for a month. In the assessment, the following parameters viz., moisture content, extractable nitrogen content, soluble hydroxyproline, hydrothermal stability, bacterial count, and visual evaluation of skins (hair slip and putrefaction odor) were assessed. The mekmeko preservation experiments were compared with parameters obtained using the conventional curing method. After 30 days of preservation, the experimental and control skins were processed into upper leather and their quality was evaluated by analyzing the physical characteristics, organoleptic properties and fiber structure using scanning electron microscope. The results showed that the curing system using 10% mekmeko powder with 15% common salt is efficient in preserving the raw goat skins. The quality of the experimental crust leathers produced from the optimized preservation system is comparable with the control leathers. The generation of the pollution load during leather processing was determined by analyzing biochemical oxygen demand, chemical oxygen demand, total dissolved solids, and chlorides from soaking liquor. Most importantly, 55% total dissolved solids and 70% chloride reduction in the soaking liquor was achieved by using the plant-based method of preservation. The less-salt preservation system based on mekmeko is a cleaner alternative for the conventional salt-based preservation method.

The transition from flocculent to granular sludge process was investigated in Sequencing Batch Airlift Reactor (SBAR) for the treatment of synthetic tannery wastewater. Chemical Oxygen Demand (COD) loading rate of 6.3 kg/m3.d and nitrogen loading rate of 0.425 kg/m3.d were applied to the reactor for 105 days using simulated tannery wastewater. The flocculent sludge was transformed to granular sludge when the operating settling time was reduced sequentially. Based on the current findings of the study, the aerobic granules formed had a MLSS concentration of 12.3 g/L, biomass density of 6.1 g /L granule, settling velocity of 30−40 m/h, SVI of 16−20 ml/g TS and size distribution in the range 1.8–3.2 mm. Evaluation of the performance of the reactor showed a very good quality effluent with average COD, NH4-N and TN removal of 97.7 ± 1.5 (%), 87.1 ± 11.8 and 74.43 ± 11.7 (%) respectively. The effect of granulation on the existence and relative abundance of selected bacteria gene involved in nitrogen cycle was analyzed by PCR and qPCR. The result confirmed the existence of AOB-amoA, nirK and PLA46+Amx820 gene. The results for qPCR also confirmed that the relative abundance of AOB-amoA and PLA46+Amx820 was higher in the reactor compared to the control.