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Multiple wastes' co-digestion is one of the alternatives for improved anaerobic digestion (AD) process of industrial and municipal wastes. The present work investigated the influence of fruit-vegetable solid waste (FVW) addition as a co-substrate on the performance of AD of abattoir wastewater (AWW). The co-digestion was done at a lab-scalebased experiment under mesophilic condition using a two-phase anaerobic sequencing batch reactor without agitation. It was tested at different mixing ratios (100%AWW; 75%AWW:25%FVW; 50%AWW:50%FVW; 25%AWW:75%FVW; 100%FVW) with the intention of looking for the best mixing ratio with the best performance. It was fed on a semicontinuous basis and operated for 18 days (d) total retention time (HRT): 3 days for the acidogenesis reactor and 15 days for methanogenesis reactor. The addition of FVW enhanced biogas yield and VS removal by 70.26% and 57.11%, respectively, at optimum mixing ratio. Moreover, to some extent improvement of AD process stability verified by the decreased TVFA:TAlk ratio and free ammonia nitrogen was observed upon progressive addition of FVW. Finally, this co-digestion process should further be studied for its performance at different HRTs with agitation.

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The Ethiopian Rift Valley Lakes Basin consists of chain of lakes, many feeder streams and wetlands with unique hydrological and ecological characteristics having regional and global environmental importance. With growing population and consequent various human activities and degradation of watersheds aggravated by climatic change, the water quality of rivers and lakes and feeder rivers are deteriorating fast. The purpose of this study is to assess physicochemical water quality parameters in two of relatively fresh water lakes (Ziway and Hawassa) which are occupying in the Central Main Ethiopian Rift floor. These parameters are pH, dissolved oxygen (DO), total dissolved solids (TDS), turbidity (NTU), Electrical conductivity (EC), and fluoride ion concentration(F -). The mean values of those physico-chemical parameters were compared with maximum permissible limit (MPL) for drinking water as standardized by the Ethiopian Ministry of Health (MoH) and the World Health Organization (WHO). The result revealed that most of the parameters show clear deterioration over the last few decades. The likely factors are rapid urbanization, sedimentation, excessive use of fertilizers and industrialization in towns established along their shorelines. Hence, these trends demand immediate intervention to avert the grave environmental consequences.