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The paper reports the results of a long term (310 days) pilot-scale trial where food waste as sole substrate was treated in a two-phase thermophilic anaerobic digestion process. This was optimized for concurrent hydrogen and methane production. First phase's optimization for hydrogen production was obtained recirculating the effluent coming from the methanogenic phase and without the addition of external chemicals. A drawback of such approach is the recirculation of ammonia into the first phase reactor for hydrogen production with possibility of consequent inhibition. Therefore this study was focused on the development of a control protocol based on ammonia concentration. The first part of this paper illustrates how the use of a variable recirculation flow makes possible to control the whole process, preventing the ammonia inhibition in the system. In order to lay down the groundwork for an automatic control of the process, in the second part of the study a preliminary statistical study is presented. In the latter are developed models to predict ammonia levels in system using the measure of Electrical Conductivity, Volatile Fatty Acids and Alkalinity. During steady state conditions, managed by a variable recirculation flow, the system produced a mixture of gas that met the standards for the biohythane mix with an average composition range of 7% H 2 , 58% CH 4 and 35% CO 2 . The overall average specific gas production (SGP) reached 0.69 m 3 Biogas /kgTVS and gas production rate (GPR) of 2.78 m 3 /m 3 r d. [ABSTRACT FROM AUTHOR]

The sustainable production of fertilizers, especially those based on phosphorus, will be one of the challenges of this century. Organic wastes produced by the agriculture, urban and industrial sectors are rich in nutrients which can be conveniently recovered and used as fertilizers. In this study five full scale systems for the recovery of nutrients from anaerobic digestate produced in farm-scale plants were studied. Monitored technologies were: drying with acidic recovery, stripping with acidic recovery and membrane separation. Results showed good performances in terms of nutrients recovery with average yields always over 50% for both nitrogen and phosphorus. The techno-economic assessment showed how the specificity of the monitored systems played a major role: in particular, membranes were able to produce a stream of virtually pure water (up to 50% of the treated digestate) reducing the digestate volume, while drying, because of the limitation on recoverable heat, could treat only a limited portion (lower than 50%) of produced digestate while stripping suffered some problems because of the presence of suspended solids in the liquid fraction treated. Specific capital and operational costs for the three systems were comparable ranging between 5.40 and 6.97 € per m 3 of digestate treated and followed the order stripping > drying > membranes. Costs determined in this study were similar to those observed in other European experiences reported in literature. [ABSTRACT FROM AUTHOR]

The integration of a methane-producing microbial electrolysis cell (MEC) into two-phase anaerobic digestion (TP-AD) was investigated, by using effluents from a pilot-scale TP-AD treating the organic fraction of municipal solid waste. The MEC was aimed at exploiting residual COD of TP-AD effluents at the MEC anode in order to support CO 2 removal and methane generation at the MEC cathode (fed by a CO 2 -rich gas phase, simulating a biogas). Feeding by 2nd phase digestate caused a loss of MEC performance, due to poor biodegradability of digestate COD under chosen anodic operating conditions (+0.2 V vs SHE, HRT 13 h, organic load 2.3 g COD/L d). On the other hand, by using the 1st phase fermentate (rich in volatile fatty acids, VFA), good MEC performance was recovered with a current of 60 ± 4 mA and a methane production rate of 33 ± 3 meq/L d. However, periodic baskwashing was also necessary to recover fouling effects. Moreover, partial nitrogen removal (228 mg N/L d) from the fermentate was obtained because ammonium was transported across the separation membrane and then recovered through the cathodic concentrated spill (at 3177 ± 97 mg N/L). Cation transport also generated net alkalinity which strongly contributed to CO 2 removal (besides methane generation). [ABSTRACT FROM AUTHOR]