• NiO nanoparticle (NP) inclusion enhanced bioethanol production up to 59.96 %. • Band energy gap impact NP catalytic performance in bioethanol production. • NiO nanoparticle biocatalyst improved bioethanol productivity by 145 %. • Modified Gompertz model was used to describe ethanol production with NP inclusion. • Metallic NiO nanoparticles significantly reduced acetic acid concentration by 110 %.

Biogas slurry (BS) is an attractive agricultural waste resource which can be used to regulate soil microbial communities, enhance nutrient absorption capacity of crops, promote plant–soil interactions, and consequently, increase crop productivity. Presently, BS discharge is not environmentally friendly. It is therefore necessary to explore alternative efficient utilization of BS. The use of BS as fertilizer meets the requirements for sustainable and eco-friendly development in agriculture, but this has not been fully actualized. Hence, this paper reviewed the advantages of using BS in farmland as soil fertilization for the improvement of crop production and quality. This review also highlighted the potential of BS for the prevention and control of soil acidification, salinization, as well as improve microbial structure and soil enzyme activity. Moreover, this review reports on the current techniques, application methods, relevant engineering measures, environmental benefits, challenges, and prospects associated with BS utilization. Lastly, additional research efforts require for optimal utilization of BS in farmlands were elucidated.

Laboratory studies were developed to compare the effectiveness of inoculated bacteria consortia and indigenous microorganisms on diesel-polluted soil for 18 days. Bacteria isolated from the unpolluted soil sample were: Pseudomonas spp. (LBI), Pseudomonas cepacia (LB5), Micrococcus luetus (LB2), Bacillus subtilis (LB3) and Bacillus cereus (LB4). Their ability to degrade different substrates were first studied by the presence of growth in minimal salt broth. All the isotates were unable to grow in hexane. LB1 and LB2 had a strong growth in n-dodecane and n-hexadecane. Only LB1, LB4 and LB5 were able to grow in paraffin. LB1 and LB5 had poor growth on xylene. LB1 and LB3 had moderate growth in phenol. All the isolates had little growth in kerosene and only LB3 and LB4 grow in diesel. The three most promising of the isolates, with moderate to strong growth (LB2, LB4 and LB5) on crude oil were further used for diesel bioremediation. The bacterial population in the augmented diesel-contaminated soil showed a reduction in the population density from days 15 to 18, an indication of nutrients (diesel oil) exhaustion. While the un-augmented diesel-polluted soil samples showed potential of more days of increased bacterial population after the 18th day of observation, a pointer of more diesel in the soil samples that can be metabolized/utilized by the microorganisms present in soil samples. The consortia of Bacillus coagulans, Citrobacter koseri and Serratia ficaria was effective in the removal of 73.8% diesel oil from the diesel-polluted soil sample while natural attenuation resulted in 41.0% diesel oil removal and 35.8% in the control. Key words: Bioaugumentation, consortia, diesel, effectiveness, pig dung, soil.

Lignocellulosic-based (LCB) bioethanol production is challenged by the presence of inhibitory compounds in pretreated LCB hydrolysates limiting productivity. The negative impact of these inhibitory compounds on LCB bioethanol production kinetics remain understudied. Hence, this study modelled the kinetics of bioethanol fermentation using nanoadsorbent-detoxified potato peel waste (PPW) hydrolysate. Four different fermentation processes under both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) conditions, including A (SHF with non-detoxified hydrolysate), B (SSF with non-detoxified hydrolysate), C (SHF with detoxified hydrolysate), and D (SSF with detoxified hydrolysate) were evaluated for bioethanol productivity. Higher productivity of 1.23 and 1.16-fold increments were recorded for fermentation processes C and D. Thereafter, the experimental data for cell growth, bioethanol production and substrate utilisation were well-fitted by the logistic function, modified Gompertz, and Luedeking-Piret models respectively. Moreover, the obtained root-mean-square error (RMSE) and mean square error (MSE) were low, while the accuracy factor (AF), bias factor (BF), slope and regression coefficient (R²) were close to 1. The bioethanol production processes were largely growth-associated (α) as α values (g ethanol/g substrate) were higher than β values (g ethanol/g substrate/h). The models were effectively implemented, demonstrating their usefulness to elucidate bioethanol productivity kinetics for improved process design and the development of large-scale bioethanol production. Graphical Abstract

This study optimized biomass and lipid accumulation using mixed dairy and paper-pulp wastewater for the cultivation of Chlorococcum sp. The obtained microalgal biomass was thereafter subjected to microwave-assisted pretreatment for optimal fermentable sugar release. Microwave power (100–700 W), pretreatment time (1–7 min), and acid-liquid ratio (1–5 %) were the input parameters for the pretreatment optimization study. The wastewater mixture ratios (25:75, 50:50, 100:0) of dairy and paper-pulp wastewater (DWW and PWW respectively) were achieved using simplex lattice mixture design to obtain high biomass and lipid accumulation in Chlorococcum sp cultivation. The model recommended a mixture of 64.69 % DWW and 35.31 % PWW for optimal biomass concentration, and a ratio of 34.21 % DWW and 65.79 % PWW for maximum lipid accumulation, predicting biomass concentration of 1.17 g/L and lipid accumulation of 0.39 g/g. Experimental validation resulted in biomass concentration and lipid accumulation 0.94 g/L and 0.39 g/g, respectively. Moreover, the experimental confirmation of the predicted fermentable sugar (11.14 g/L) yielded 15.67 g/L with pretreatment set points of 2.52 % HCl for 4.06 min at 700 W. Additionally, the prospect of the optimized pretreated microalgal biomass for bioethanol production (7.85 g/L) was achieved. Findings from this study could facilitate the implementation of DWW and PWW wastewaters utilization that could significantly lower the use of scarce potable water in keeping with portable water, energy, and environmental sustainability nexus towards the realisation of a circular bioeconomy.