Currently, there are challenges with proper disposal of cassava processing wastewater, and a need for sustainable energy in the cassava industry. This study investigated the impact of co-digestion of cassava wastewater (CW) with livestock manure (poultry litter (PL) and dairy manure (DM)), and porous adsorbents (biochar (B-Char) and zeolite (ZEO)) on energy production and treatment efficiency. Batch anaerobic digestion experiments were conducted, with 16 treatments of CW combined with manure and/or porous adsorbents using triplicate reactors for 48 days. The results showed that CW combined with ZEO (3 g/g total solids (TS)) produced the highest cumulative CH4 (653 mL CH4/g VS), while CW:PL (1:1) produced the most CH4 on a mass basis (17.9 mL CH4/g substrate). The largest reduction in lag phase was observed in the mixture containing CW (1:1), PL (1:1), and B-Char (3 g/g TS), yielding 400 mL CH4/g volatile solids (VS) after 15 days of digestion, which was 84.8% of the total cumulative CH4 from the 48-day trial. Co-digesting CW with ZEO, B-Char, or PL provided the necessary buffer needed for digestion of CW, which improved the process stability and resulted in a significant reduction in chemical oxygen demand (COD). Co-digestion could provide a sustainable strategy for treating and valorizing CW. Scale-up calculations showed that a CW input of 1000–2000 L/d co-digested with PL (1:1) could produce 9403 m3 CH4/yr using a 50 m3 digester, equivalent to 373,327 MJ/yr or 24.9 tons of firewood/year. This system would have a profit of $5642/yr and a $47,805 net present value.
Heavy metals are pollutants of river sediments, and their concentration varies depending on parental material and anthropogenic inputs, thus important to distinguish between the natural and anthropogenic inputs. The objective of this study is to use different types of indexes to assess the current pollution status in Ogbere River sediment and select the best index to describe the sediment quality. The indexes used in this study were enrichment factor (EF), geoaccumulation index (Igeo) and principal component analysis (PCA). The PCA has an advantage over other index analyses as it reduces the dimensionality of the data set and thus used to support multivariate cluster analysis. From the study, a total of 12 sediment samples were collected in both seasons across six sampling location and pollution indexes indicated three things: firstly, the metal distribution profile in the sediment showed that the heavy metals analysed for were lower than the maximum allowable limits stipulated by Department of Petroleum Resources (DPR); secondly, minor to extremely severe significant levels of enrichment and thirdly, practically uncontaminated to a moderately contaminated degree of contamination in Ogbere River during the study period. The PCA is considered more sensitive in the analysis of benthic changes and as well as sediment quality. However, the heavy metal assessment indices are not only used for sediment quality. Biological testing and ecological analysis of existing community related to sediment contamination are further recommended in River Ogbere.
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