Agro-industrial wastewaters are known by high strength of organic pollutants that cause an adverse effect on the water bodies. Wastewater management becomes a major task, leads environmental regulations to be stricter worldwide. Increased disposal of untreated/partially treated industrial wastewaters are major environmental problems in Ethiopia. In Ethiopia, industries most commonly dispose their untreated wastewater straight into the nearby rivers. Somewhat, constructed wetlands are used by some industries for treatment of wastewaters. The objective of this review paper was to summarize the characteristics and recent research efforts done on anaerobic treatment of some selected agro-industrial wastewaters and innovative technologies used for cogeneration of byproducts. Many developed countries designed cost effective approaches for agro-industrial wastewater management. The full-scale anaerobic treatment system in China generates 40,000 m³ biogas daily for 20,000 households from agro-industrial wastes. Likewise, the Brewery, Addis Ababa, Ethiopia used full-scale anaerobic treatment technology and produce average methane yield of 487 Nm³/day. The estimated maximum methane production potential of Kera, Luna slaughterhouses, and Ada milk factory were 4.5599LCH₄, 0.1878LCH₄, and 0.9952LCH₄, respectively. These indicate that they can be potential sources of biogas production. Limitations of the brewery are burning of the produced energy and some quantified parameters being become above national standards while meat processing and diary industries are discharging their wastewater without treatment into the rivers. We devised the brewery to use the produced energy properly and extend its treatment to achieve the national standards using integrated sequencing batch reactor. Similarly, slaughterhouse and diary industries should install anaerobic–aerobic integrated treatment techniques.

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.

Chromium (Cr) is a heavy metal that has a serious environmental pollution problem. Electroplating wastewater contains high level of Cr that surpassed the acceptable environmental discharge standard limit in surface water bodies and causes aquatic ecosystem risks. Various studies have been conducted in Ethiopia on the removal of Cr from various types of wastewater; however, factual studies on the adaptability of cost-effective activated coffee husk carbon for the removal of Cr from electroplating wastewater are lacking. Thus, this study was conducted to evaluate the Cr adsorption efficiency of activated coffee husk carbon from electroplating wastewater at laboratory scale. The activated coffee husk carbon’s pH, electrical conductivity (EC), ash content, moisture content, bulk density, particle size, pore volume, porosity, volatile organic matter, carbon yield, and carbon:nitrogen ratio were determined following standard methods. In the adsorption experiment, adsorbent dosage, agitation speed, contact time, pH, and initial concentration were optimized. Models were used to examine the adsorption isotherms and kinetics. The ability of activated coffee husk carbon to desorb Cr was investigated. The adsorbent functional groups and surface morphology were examined using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM), respectively. Analysis of the physicochemical characteristics of the adsorbent showed that the activated coffee husk carbon has good quality, and thus, playing an important role in metal adsorption. Furthermore, FTIR analysis also confirmed the presence of hydroxyl, carboxyl, and other important functional groups, which promote heavy metal adsorption. The adsorption process optimization revealed 99.65% maximum Cr adsorption efficiency at 120 min contact time, 40 mgL^-1 initial concentration, 150 rpm agitation speed, pH 7.0, and 20 gL^-1 adsorbent dosages. From the adsorption model studies, Freundlich sorption isotherm and pseudosecond-order models were well fitted with respective [ ] values of 0.987 and 0.999. A 60% Cr was removed according to desorption studies. In general, due to the ease with which coffee husk can be obtained from coffee processing facilities, its use as an absorbent will be cost-effective and considered as an alternative option in removing Cr metal from wastewaters.

Tomato (Solanum lycopersicum) is one of the most widely cultivated and economically important vegetable crops worldwide, contributing significantly to food security. However, its low productivity remains a substantial concern in Ethiopia due to mainly poor soil quality and limited use of inorganic fertilizers. On the contrary, improper disposal of recyclable charcoal and anaerobic cow dung bioslurry (ACDB) wastes poses environmental pollution challenges. Hence, this study aimed to evaluate the synergetic effects of ACDB and charcoal co-composted fertilizers (ACDBCFs) on tomato productivity and soil properties. A pot experiment consisting of eight treatments (T1 - T8) was arranged in a randomized complete block design with three replications. Characterization of the five formulated ACDBCFs revealed good physico-chemical properties of pH, organic carbon, ammonium, nitrate, and orthophosphate, fluctuated from 8.9 to 9.63, 26.8 to 65.6%, 2.5 to 4.6 mgL ⁻ 1, 11.9 to 18.2 mgL ⁻ 1, and 0.74 to 3.1 mgL ⁻ 1, respectively. Significant differences (p < 0.05) were observed in tomato fruit yield with relatively higher values of 2.87 and 2.73 kgpot ⁻ 1 for T6 and T8 under ACDB + charcoal (+10%) and inorganic fertilizers amendments, respectively. Principal component analysis (PCA) demonstrated strong associations between nutrient availability and tomato growth and yield component parameters. Heat map visualization further confirmed that ACDBCFs application improved soil background nutrient and carbon contents. Overall, the findings from this short-term study indicate that ACDBCFs can enhance tomato productivity while improving soil organic matter and nutrient availability. However, further long-term studies on field level validation in real soil conditions and nutrient dynamics are recommended to support large-scale adoption of this resource-recovery approach, contributing to sustainable agriculture, environmental protection, and socio-economic development.