No abstract

The importance of the balance between the nutrients in the anaerobic digestion process was assessed at laboratory scale. A soluble synthetic solution was used as substrate. The variable used to monitor the proportion of nutrients in the substrate was the [C]/[N + P] ratio expressed as equivalents of each element. A blank assay with a constant ratio of 53 and three experiments in which this variable was modified in the range 53–1 were performed. An increase in the concentration of nitrogen and phosphorus both separately and in combination was observed. The most relevant results show a loss of N in the biogas in the form of NH3 for concentrations of around 400 mg N soluble/L in the liquid phase of the reaction, and a loss of soluble phosphorus in the form of calcium phosphate due to precipitation at concentrations above 250 mg P soluble/L, regardless of the experimental procedure. No significant effects were observed in the production of biogas for a ratio in the range 53–40, while biogas production decreased by 8% for a ratio of 20 when both N and P increased in the best of cases and by up to 46% when only N increased. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 228–236, 2019

No abstract

Greenhouse cultivation has significantly increased the production of vegetables and reduced dependence on environmental conditions. In Mediterranean areas, vegetable crops are nowadays one of the most important sources of organic waste generation. Anaerobic digestion is among the methods used to treat this type of biodegradable waste. However, the selection of the organic wastes to be subjected to this microbial treatment is a crucial aspect due to seasonality and simultaneity of the original crops. In this sense, as waste does not have frequently the proper nutrient balance, co-digestion with other substrates generated in the same geographical area is recommended to ensure the correct development of the process. This work studies the mesophilic co-digestion of tomato waste (TW) and cucumber waste (CW), which are common greenhouse wastes that do not contain an adequate ratio among nutrients (C/N/P) and are generated simultaneously. The influence of the percentage of both wastes in the mixture on the overall performance of the process was evaluated. The combination of TW and CW was found to be feasible in terms of stability, biodegradability and methane yield, which reached a value of 292 mLSTP CH4/g VS (STP: standard temperature and pressure, 0°C and 760 mmHg) for the percentage of tomato in the mixture, which is considered optimal at 55-75%. The most suitable organic load rate was determined for a percentage of 65% of TW, reaching a value of 1562 kg(waste) m(-3) month(-1).

No abstract