Little Akaki River drains residential, industrial, and agricultural irrigation areas of Addis Ababa City Administration and is exposed to point and non-point sources of pollution. The purpose of this study was to identify sources, evaluate the levels of river water pollution, and its implications for environmental and public health. Pollution indices and multivariate statistical analyses were used to determine sources and levels of the river water pollution. Trace metals concentration was determined using inductive coupled plasma optical emission and spectrophotometer (ICP-OES). The average concentrations of COD, BOD, TDS, NO3–N, NH3–N, SO4−2, and PO4−3 ranged from 40. 33 ± 5. 13 to 425 ± 8. 00 mg/L; 12.34 ± 0.11 to 188 ± 7.07 mg/L; 48.00 ± 0.83 to 915. 57 ± 1. 27 mg/L; 1.56 ± 1.01 to 66.50 ± 6.36 mg/L; 0.15 ± 0. 08 to 42.83 ± 11.43 mg/L; 20.50 ± 10.61 to 77.50 ± 17.68 mg/L; and 0.35 ± 0.33 to 37.95 ± 0.92 mg/L, respectively. The average concentrations of Zn ranged (0.048 ± 0.037 to 0.318 ± 0.158 mg/L), Cr (0.012 ± 0.007 to 0.203 ± 0.199 mg/L), Cd (2.01). Heavy metal pollution index values further demonstrated potential environmental and public health implications. The principal component analysis revealed a total of 88.99% variation in the dataset, mainly contributed by organic matter, nutrients, dissolved salts, and trace metals that originated from anthropogenic sources. Contamination of the river water has impaired its suitability for urban agriculture, aquaculture, livestock drinking, and recreational purposes. Thus, improving the river water quality is recommended to mitigate potential adverse effects and promote sustainable use of water resources.

Wastewater sludge generated from agro-industrial wastewater treatment plants is accepted as a good option for land application as a soil conditioner and substitute mineral fertilizers. However, the quality of the sludge sometimes posed a threat to the surroundings. The objective of the study is to evaluate the biochemical characteristics and fertilizer potential of brewery wastewater sludge for agricultural reuse. A field experiment was conducted in a randomized block design array with three replications using brewery wastewater sludge, and nitrogen, phosphorus and sulfur (NPS) containing commercial fertilizer along with control treatments. The result showed that sludge application significantly increased average above biomass production by 5.7% and 37.2% over the NPS and control plots, respectively. Also, the sludge-amended plot produced more grain yield of maize with 26.8% greater than the control. The brewery sludge temporary residual effect analysis revealed that the addition of the sludge led significant changes in soil pH reduction and soil electrical conductivity, total phosphorus, total nitrogen and total potassium increment as compared to others and background concentration. Similarly, lead and fecal coliform concentrations in the sludge-amended soil showed 150% and 24.4% increments, respectively, over the control. In general, the preliminary sludge temporary residual effect analysis showed an encouraging outcome on soil basic properties and maize crop productivity. Conversely, future long-term study is essential to monitor the effect of soil salinity, heavy metal and pathogen contaminations on soil and crop production.

The anaerobic process is considered to be a sustainable technology for the treatment of wastewaters rich in organic matter mainly due to its lower energy consumption and production of value-added products such as biogas and organic fertilizer. However, it cannot be seen as providing ‘complete’ environmental solution as its treated effluents would typically not meet the desired discharge limits in terms of residual carbon, nutrients and other pollutants. This has given impetus to subsequent post treatment in order to meet the environmental standards and protect the receiving water bodies and environment. The aim of this study was to evaluate the post-treatment potential of a pilot scale two-stage horizontal subsurface flow constructed wetland (HSSFCW) system planted with Cyperus alternifolius and Typha latifolia, respectively, for enhanced removal of residual carbon and nutrient from an up-flow anaerobic sludge blanket (UASB) reactor treated brewery effluent. A pilot scale two-stage HSSFCW was integrated with the UASB reactor, and its performance efficiency was assessed for the removal of total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), ammonium–nitrogen (NH₄–N), total phosphorous (TP), and orthophosphate (PO₄³⁻). Macrophytes aboveground biomass and nutrient accumulation potential were also determined following standard methods. The results from this study showed that Cyperus alternifolius planted CW cell removed 68.5% TSS, 74.2% COD, 55.7% TN, 68.6% NH₄–N, 41.1% TP and 48.1% PO₄³⁻. Moreover, further polishing with Typha latifolia planted CW cell enhanced the removal efficiencies to 89% TSS, 92% COD, 83.6% TN, 92.9% NH₄^–N, 74.4% TP, and 79.5% PO₄³⁻. Strong linearity and Pearson correlation was found between macrophyte biomass and nutrient accumulation in each CW cell (Cyperus alternifolius: R² = 0.91, r = 0.97 for TN; R² = 0.92, r = 0.96 for TP; and Typha latifolia: R² = 0.96, r = 0.98 for TN and TP), and showed substantial nutrient reduction with cumulative nutrient accumulation of 1290 gTNm⁻² and 708.7 gTPm⁻² in the complete system. The performance of the pilot CW system as a tertiary treatment for brewery wastewater showed that the effluent meets the permissible discharge standards throughout the year excluding phosphorous.

The objective of the present study was an optimization of operating parameters and the performance of the methanogenesis reactor in phased anaerobic digestion (AD) of slaughterhouse wastewater at 37.5°C. Accordingly, the feedstock of the methanogenic reactor was effluent from the hydrolytic-acidogenic reactor operating at HRT of 3-days and OLR of 1789 mg/L. The methanogenesis phase was also investigated at different hydraulic retention time (HRT) values ranging from 12 to 3 days at 3-day intervals, and organic loading rates (OLR) of 149, 199, 298, and 596 mg of COD/L. The methanogenesis reactor effluent concentrations of TN, TP, PO₄^− 3, SO₄^− 2, and S₂^− 2 were ranging between 424–464, 83–117, 63–86, 130–197, and 0.98–1.02 mg/L, respectively. The removal efficiencies of TN and TP were vary from 10–17% to 17–21%, respectively. The average biogas production was 125 ± 16, 150 ± 10, 185 ± 4, and 154 ± 17 mL at HRT of 12, 9, 6, and 3 days, respectively. Methane quality (%) and yield (mg/L of COD) were 55–67% and 0.02–0.03, respectively. Furthermore, the average stability indicator parameter values of (total volatile fatty acid (TVFA) = 520 ± 19 mg/L, total alkalinity (TotA) = 1424 ± 10 mg/L, TVFA:TotA. Ratio = 0.36, salinity = 1172 mg/L, pH = 6.92) and performance indicator parameters removal efficiency (RE) for (chemical oxygen demand (COD) = 81%, volatile solid (VS) RE = 95%, biogas production = 185 ± 4 mL, methane yield = 0.03 per mg COD consumed) were achieved at HRT of 6 days and OLR of 298 mg of COD/L. Low removal efficiencies of TP and TN at all HRT/OLR were observed for the methanogenic reactor signifying further treatment system. Graphical Abstract

In a two-phase anaerobic digestion process, enhanced biogas production and organic pollutant removal depend on the stability and performance of the hydrolytic–acidogenic and methanogenic phases. Additionally, the hydrolytic–acidogenic phase is a rate-limiting step, which calls for the further optimization of operating parameters. The objective of this study was to optimize the operating parameters of the hydrolytic–acidogenic reactor (HR) in the two-phase anaerobic digestion treating slaughterhouse wastewater. The experiment was carried using bench-scale sequential bioreactors. The hydrolytic–acidogenic reactor operating parameters were optimized for six different hydraulic retention times (HRTs) (6–1 day) and organic loading rates (OLRs) (894.41 ± 32.56–5366.43 ± 83.80 mg COD/L*day). The degree of hydrolysis and acidification were mainly influenced by lower HRT (higher OLR), and the highest values of hydrolysis and acidification were 63.92% and 53.26% at an HRT of 3 days, respectively. The findings indicated that, at steady state, the concentrations of soluble chemical oxygen demand (SCOD) and total volatile fatty acids (TVFAs) decrease as HRT decreases and OLR increases from HRTs of 3 to 1 day and 894.41–1788.81 mg COD/L*day, respectively, and increase as the HRT decreases from 6 to 4 days. The concentration of NH₄⁺-N ranges from 278.67 to 369.46 mg/L, which is not in the range that disturbs the performance and stability of the hydrolytic acidogenic reactor. It was concluded that an HRT of 3 days and an ORL of 1788.81 mg COD/L*day were selected as optimal operating conditions for the high performance and stability of the two-phase anaerobic digestion of slaughterhouse wastewater in the hydrolytic–acidogenic reactor at a mesophilic temperature. The findings of this study can be applicable for other agro-process industry wastewater types with similar characteristics and biowaste for value addition and sustainable biowaste management and safe discharge.