Lab-scale anaerobic digestion of cassava peels: the first step of energy recovery from cassava waste and water hyacinth

Effect of floating treatment wetland coverage ratio and operating parameters on nitrogen removal: toward design optimization

Floating treatment wetlands (FTWs) have the potential to improve the quality of wastewater discharges, yet design basics are unavailable to size these systems. This study investigates the effect of FTWs' coverage ratio and hydraulic retention time on agri-food wastewater treatment. This was studied in a pilot-scale experiment comprising four lagoons (6.5 m3 each) fed with real effluent from an existing tertiary treatment lagoon. An evaluation of FTW of different sizes (L24, L48, and L72 representing 24, 48, and 72% of pilot lagoons surface areas) and a control, L0 (without FTW), was performed over 16 months. Overall, L72 and L48 moderately improved total nitrogen (TN) mass removal compared to L0 (p < 0.05), while L24 exhibited similar TN mass removal (p = 0.196). The highest improvement was observed for L72, exhibiting up to 55% (mean of 13%) greater N mass removal than the control. The net increase in TN removal by FTWs was mainly related to denitrification, promoted by decreasing dissolved oxygen for increasing FTW coverage ratio. Residence time, temperature, and dissolved oxygen were the main parameters driving TN removal by FTWs. Retrofitting existing lagoons with FTW can facilitate N retrieval through plant harvesting, thereby reducing N remobilization from sediment (common in conventional lagoons).

Valorization of agricultural wastes for biofuel applications

Continuous environmental degradation, volatility in the oil market, and unimpressive functioning of fossil-based (FB) fuels in compression ignition engines have expanded the tempo of the search for alternative fuels. Due to the astronomical rise in global population, improved agricultural, commercial, and manufacturing activities, enhanced farming and other food production and utilization ventures, agricultural waste generation, renewable fuel consumption, and emission of toxic gases. The need for cost-effective, readily available, and environmentally benign agricultural waste to biofuels has never been more crucial. Biofuels are renewable, biodegradable, low-cost, and eco-friendly fuels that are produced by microorganisms from waste lignocellulosic biomass. Conversion of agricultural wastes to biofuel does not exacerbate food security, contributes to waste management, prevents environmental degradation, and ensures energy security. This study reviews the conversion of agricultural wastes into biofuels with special emphasis on bioethanol, biohydrogen, biobutanol, biomethane, biomethanol, and biodiesel for various applications. It is safe to conclude that wastes generated from agricultural activities and processes are useful and can be harnessed to meet the affordable and accessible global renewable energy target. The result of this investigation will improve the body of knowledge and provide novel strategies and pathways for the utilization of agricultural wastes. Going forward, more collaborative and interdisciplinary studies are required to evolve state-of-the-art, ecofriendly, and cost-effective conversion pathways for agricultural wastes to promote the utilization of the generated renewable fuels. More human, financial, and infrastructural investments are desirable to motivate the conversion of agricultural waste into biofuels to ensure environmental sanitation and sustainability, promote renewable fuel utilization, and avert the raging implosion of our planet.

Anaerobic digestion of urban wastes: integration and benefits of a small-scale system

This work presents an integrated approach of anaerobic digestion (AD) at the urban scale, based on on-site collected wastes, experimentation in a pilot reactor, and model approach. To cope with urban waste limitations (season inflow, organic matter decrease, limited area), it was proposed a settlement of wastewater (WW), a drying of food waste (FW), and silage of green waste (GW). The results obtained highlight the performance of these pretreatments to concentrate and/or preserve the organic matter over time. Co-digestion in a 30-liter reactor was then successfully carried out, resulting in an 83% of volatile solids reduction and stable methane production of 321 ml CH₄/g VS_add, in 35 days. Finally, we developed a standard neighbourhood model with AD based on these experimental results. It appears that 66% of the primary sludge (PS) and 28% of the FWs produced daily could be treated by the proposal process. 14% of the annual production of GW could thus be processed daily. From an energetic point of view, the process generates a surplus of respectively, 2500 MJ/year and 38,000 MJ/year in terms of electricity and heat. The generation of 15 times more heat energy than electricity, supports an installation of anaerobic digestion, close to homes. Moreover, if these results are encouraging, we suggest different scenarios of co-digestion ratios and operational parameters for their optimization.