Sustainable Management of Organic Wastes in Sharjah, UAE through Co-Composting

Biochar addition influences C and N dynamics during biochar co-composting and the nutrient content of the biochar co-compost

This study investigated the effects of corn cob biochar (CCB) and rice husk biochar (RHB) additions (at 0%, 5%, and 10% w/w) on nitrogen and carbon dynamics during co-composting with poultry litter, rice straw, and domestic bio-waste. The study further assessed the temperature, moisture, pH, and nutrient contents of the mature biochar co-composts, and their potential phytotoxicity effects on amaranth, cucumber, cowpea, and tomato. Biochar additions decreased NH4+-N and NO3- contents, but bacteria and fungi populations increased during the composting process. The mature biochar co-composts showed higher pH (9.0-9.7), and increased total carbon (24.7-37.6%), nitrogen (1.8-2.4%), phosphorus (6.5-8.1 g kg-1), potassium (26.8-42.5 g kg-1), calcium (25.1-49.5 g kg-1), and magnesium (4.8-7.2 g kg-1) contents compared to the compost without biochar. Germination indices (GI) recorded in all the plants tested with the different composts were greater than 60%. Regardless of the biochar additions, all composts treatments showed no or very minimal phytotoxic effects on cucumber, amaranth and cowpea seeds. We conclude that rice husk and corn cob biochar co-composts are nutrient-rich and safe soil amendment for crop production.

Literature review on the potential of urban waste for the fertilization of urban agriculture: A closer look at the metropolitan area of Barcelona

Urban agriculture (UA) activities are increasing in popularity and importance due to greater food demands and reductions in agricultural land, also advocating for greater local food supply and security as well as the social and community cohesion perspective. This activity also has the potential to enhance the circularity of urban flows, repurposing nutrients from waste sources, increasing their self-sufficiency, reducing nutrient loss into the environment, and avoiding environmental cost of nutrient extraction and synthetization. The present work is aimed at defining recovery technologies outlined in the literature to obtain relevant nutrients such as N and P from waste sources in urban areas. Through literature research tools, the waste sources were defined, differentiating two main groups: (1) food, organic, biowaste and (2) wastewater. Up to 7 recovery strategies were identified for food, organic, and biowaste sources, while 11 strategies were defined for wastewater, mainly focusing on the recovery of N and P, which are applicable in UA in different forms. The potential of the recovered nutrients to cover existing and prospective UA sites was further assessed for the metropolitan area of Barcelona. Nutrient recovery from current composting and anaerobic digestion of urban sourced organic matter obtained each year in the area as well as the composting of wastewater sludge, struvite precipitation and ion exchange in wastewater effluent generated yearly in existing WWTPs were assessed. The results show that the requirements for the current and prospective UA in the area can be met 2.7 to 380.2 times for P and 1.7 to 117.5 times for N depending on the recovery strategy. While the present results are promising, current perceptions, legislation and the implementation and production costs compared to existing markets do not facilitate the application of nutrient recovery strategies, although a change is expected in the near future.