-The aim of the present study was to evaluate the efficacy of treating vinasse using anaerobic digestion (AD) followed by ozonation. The AD process was performed using a laboratory-scale upflow anaerobic filter reactor (UAFR) under continuous operation at 29 ± 1 °C. Stable conditions were reached at 10 kgCOD m -3 d -1 and a hydraulic retention time (HRT) of 5 days. Under these conditions, the efficiency of reduction of the chemical oxygen demand (COD) and the methane yield were 75.1% and 0.315 m 3 CH 4 kgCODr -1 , respectively. The anaerobically digested effluent was further treated using ozone in a bubbling column. An experimental 2 3 array [C(0 3 ) g = 70; 100 mgO 3 L -1 ; pH= 7.5; 10; tc = 1 and 3 h] was used. The best conditions for effluent ozonation were 100 mgO 3 L -1 , pH 7.5 and 3 hours of contact with ozone. The average efficiencies for COD, color and turbidity reduction were 82.4, 93.8 and 99.3%, respectively.

The effect of natural mineral on the mono-digestion of maize straw was evaluated in continuously stirred tank reactors (CSTRs) at 38 °C. Different strategies of mineral addition were studied. The organic loading rate (OLR) was varied from 0.5 to 2.5 g volatile solid (VS) L(-1) d(-1). A daily addition of 1 g mineral L(-1) in reactor 2 (R2) diminished the methane production by about 11 % with respect to the initial phase. However, after a gradual addition of mineral, an average methane yield of 257 NmL CH4 g VS(-1) was reached and the methane production was enhanced by 30 % with regard to R1. An increase in the frequency of mineral addition did not enhance the methane production. The archaeal community was more sensitive to the mineral than the bacterial population whose similarity stayed high between R1 and R2. Significant difference in methane yield was found for both reactors throughout the operation.

The anaerobic treatment of raw vinasse in a combined system consisting in two methanogenic reactors, up-flow anaerobic sludge blanket (UASB) + anaerobic packed bed reactors (APBR), was evaluated. The organic loading rate (OLR) was varied, and the best condition for the combined system was 12.5 kg COD mday with averages of 0.289 m CH kg COD rfor the UASB reactor and 4.4 kg COD mday with 0.207 m CH kg COD r for APBR. The OLR played a major role in the emission of HS conducting to relatively stable quality of biogas emitted from the APBR, with HS concentrations <10 mg L. The importance of the sulphate to COD ratio was demonstrated as a result of the low biogas quality recorded at the lowest ratio. It was possible to develop a proper anaerobic digestion of raw vinasse through the combined system with COD removal efficiency of 86.7% and higher CH and a lower HS content in biogas.

The influence of the bonding form distribution of Fe, Ni, Co and Mn and their potential bioavailability during the anaerobic degradation of maize straw was investigated. Two reactors were operated over 117 days at 37°C and different dosage strategies of mineral were studied in reactor (R2). Control reactor (R1) was metal‐limited over time. mineral supplementation (1 g L−1) once a week reported the highest methane yield (257 mL g−1 VS) with 30% of increment. Ni and Co predominated in their oxidizable bonding forms and Fe mainly existed as residual and oxidizable fractions. The potential bioavailability (Mn ˃˃ Co ≈ Ni ˃ Fe) of R2 was higher comparing to R1. Metal deprivation in R1 led to depletion of both sequential extraction fractions and total metal concentrations until the end of the process. This study confirmed that the dosage strategy of mineral has a stimulatory effect on methane production from crop maize waste.

This paper studied the effect of adding an enzyme ( ellulose) on anaerobic digestion of maize silage. We compared materials at chopping lengths of 8 mm (MSL), 4mm (MSS) and natural size (Ms) under a mesophilic and discontinuous operation (batch process). Hence, we found the process to be significantly influenced by particle size. Moreover, the ellulose addition did not significantly impact biogas production after a 35-day digestion period. Ms and MSS displayed an improved response to all variables when compared with MSL and MSL+C, with significant differences. Studies on the refractory fraction at infinite time (R 0 ) have demonstrated that the lowest values correspond to Ms and MSS (0.122 and 0.155, respectively

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This paper shows the effect of organic shock loads (OSLs) on the anaerobic digestion (AD) of synthetic swine wastewater using an expanded granular sludge bed (EGSB) reactor modified with zeolite. Two reactors (R1 and R2), each with an effective volume of 3.04 L, were operated for 180 days at a controlled temperature of 30 °C and hydraulic retention time of 12 h. In the case of R2, 120 g of zeolite was added. The reactors were operated with an up-flow velocity of 6 m/h. The evolution of pH, total Kjeldahl nitrogen, chemical oxygen demand (COD) and volatile fatty acids (VFAs) was monitored during the AD process with OSL and increases in the organic loading rate (OLR). In addition, the microbial composition and changes in the structure of the bacterial and archaeal communities were assessed. The principal results demonstrate that the presence of zeolite in an EGSB reactor provides a more stable process at higher OLRs and after applying OSL, based on both COD and VFA accumulation, which presented with significant differences compared to the control. Denaturing gradient gel electrophoresis band profiles indicated differences in the populations of Bacteria and Archaea between the R1 and R2 reactors, attributed to the presence of zeolite.

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