Anaerobic co-digestion(AcoD) of active sludge (AS) and olive mill wastewater (OMW) is becoming an increasingly recognized alternative to manage waste and generate renewable energy. A kinetic study of the performance of biochemical methane potential (BMP) and continuous stirred tank reactors (CSTR) bioreactors was conducted to identify critical parameters influencing. Substrates of 100%OMW, 100%AS, 25:75%, 75:25%, and 50:50 were utilized in the BMP and CSTR digesters. To identify the optimum mixing, BMP tests were conducted under three different operating conditions: no mixing (NM), low-continuous mixing intensity (LM) of 25 rpm, and high continuous mixing intensity (HM) of 60 rpm. CSTR with an optimum mixing regime is utilized to identify the optimum substrate. In particular, the removal efficiency of volatile solids (VSs), total chemical oxygen demand (TCOD), and the production of biogas and methane (CH4) were investigated to specify the performance of the anaerobic digestion (AD) process. The results revealed that the optimum mixing regime is LM with BMP tests. Also, the maximum performance in CSTR-ML was achieved by 75:25 AS:OMW, 0.339 Nm3/kg VS of biogas, 69.89% of CH4, and a removal efficiency of 87.12% of VS and 79.23% of TCOD. For BMP tests, the biogas and CH4 yield production kinetics were best fitted by the modified Gompertz models: mono-digestion and co-digestion 75:25 and 50:50 of AS:OMW, while the best-fit model for co-digestion 25:75 was achieved by the transfer model. The production kinetics were well described by modified Gompertz models in CSTR tests. These results point to the possibility of optimizing digester systems on a wide scale using the outputs that have been observed. Novelty statement. This research work provides novel insights into the performance of the digester under diverse mixing conditions and varying co-substrate concentrations of AS:OMW and presents the best model to predicate the biogas and CH4 at various operation conditions.

The impacts of nanoparticles-zerovalent iron (NP-ZVI) on anaerobic co-digestion (AcoD) were assessed. The production of biogas and methane (CH₄), as well as the removal efficiency of volatile solids (VS) and contaminants were investigated in the AcoD of chicken manure (CM) and olive mill wastewater (OMWW) with the addition of NP-ZVI at different concentrations (10–50 mg/g VS) and different sizes resulting from various mixing volume ratios (MVR) of NaBH₄:FeSO₄.7H₂O. The results show that NP-ZVI ≤ 30 mg/g VS at MVR-2:1, MVR-4:1, and MVR-6:1 improves the AcoD. In contrast to 40–50 mg/g VS of NP-ZVI, which caused an inhibitory impact in all of the AcoD stages, as well as a decrease in the contaminant’s removal efficiency, the concentration of 10–30 mg NP-ZVI/g VS at MVR-4:1 achieved a maximum improvement of CH₄ by 21.09%, 20.32%, and 22.87%, respectively, and improved the biogas by 48.14%, 55.0%, and 80.09%, respectively, vs. the 0 additives. Supplementing AcoD with NP-ZVI at a concentration of 30 mg/g VS at MVR-4:1 resulted in maximum enhancement of the contaminant removal efficiency, with a total oxygen demand (TCOD) of up to 73.99%, turbidity up to 79.07%, color up to 53.41%, total solid (TS) up to 59.57%, and volatile solid (VS) up to 74.42%. It also improved the hydrolysis and acidification percentages by up to 86.67% and 51.3%, respectively.

The technique of multi-stage desalination with brine recirculation (MSF-BR) is characterized by its high energy demand, necessitating the exploration of efficient operational methods to minimize energy consumption and enhance plant performance. In this research study, Matlab R2021a software was used to apply a genetic algorithm with the aim of determining the optimal values of the operating variables of the MSF-BR system within certain limits, considering energy consumption and feed seawater temperature variation. The study included improving several operational factors, including top brine temperature, steam temperature, feed seawater temperature, cooling water flow rate and make up flow rate, number of station stages, and the stages of the heat rejection section. The optimal maintenance period during the operational year was also determined. The results of the analysis were based on data from the Al-Khafji desalination plant, which consists of 16 stages and has a production capacity of 7,053,393.8 gallons/day. The study aimed to achieve two main objectives: increasing the gain output ratio (GOR) and reducing the proportion of the recovery ratio. The results showed that the optimal period for maintenance is January, where the performance ratio ranges between 0.987 and 9.38, compared to the currently used month of December, where the performance ratio ranges between 1.096 and 9.56. Optimal target values were set at the following operating parameters: 33.3 °C for feed seawater temperature, 98.67 °C for steam temperature, 95.62 °C for brine temperature, 1571.18 kg/s for cooling water flow rate, 1624.24 kg/s for feed water flow rate, 21 stages for the station, and two stages for the heat rejection section. To achieve the highest GOR, the number of stages and heat rejection section should be more than 19 and 2, respectively. In general, to achieve improvements in GOR and reduce energy consumption, it is recommended to maintain Tf in the range of 33–34 °C and set M_cw between 1050 and 1800 kg/s.

This study evaluates the potential of spent coffee grounds (SCGs) as a co-substrate to improve anaerobic co-digestion (AcD) performance, with a focus on biogas yield, methane (CH₄) content, and the removal of volatile solids (VS) and total chemical oxygen demand (TCOD). Biochemical methane potential (BMP) tests were conducted in two stages. In Stage I, SCGs were blended with active sludge (AS) and the organic fraction of municipal solid waste (OFMSW) at varying ratios. The addition of 25% SCGs increased biogas production by 24.47% (AS) and 20.95% (OFMSW), while the AS50 mixture yielded the highest methane yield (0.302 Nm³/kg VS, 66.42%). However, SCG concentrations of 75% or higher reduced process stability. In Stage II, we evaluated the impact of mixing. The AS25 configuration maintained stable biogas under varying mixing conditions, showing system resilience, whereas OFMSW25 showed slight improvement. Biogas production kinetics were modeled using modified Gompertz, logistic, and first-order equations, all of which demonstrated high predictive accuracy (R² > 0.97), with the modified Gompertz model offering the best fit. Overall, SCGs show promise as a sustainable co-substrate for the improvement of methane recovery and organic matter degradation in AcD systems when applied at optimized concentrations.