Abstract
A hybrid anaerobic reactor was operated under the complementary effluents concept to reduce the unbalanced/inhibitory capacity of the provided piggery effluent. Brewery wastewater was chosen to complement piggery effluent (60:40% v/v, respectively). The HRT reduction from 6.7 to 3.0 days allowed the testing of an organic load increase from 4.5 to 10.0 g COD/L·d, which resulted in the almost doubling of biogas production. Biogas volumes (1.2 and 2.1 L/L·d, respectively) associated with its quality (>77% CH4) revealed that the hybrid anaerobic reactor responded positively to the operational changes and that piggery effluent can be advantageously digested using the brewery wastewater as the complementary effluent. The unit bottom and the packing bed were the main functional sections recognized in the hybrid. At the beginning of anaerobic digestion, bacterial populations belonged mostly to Bacteroidales (33%) and Clostridiales (35%). The process stability and the biogas quality at 3-d HRT were related to a change in the structure composition, since Flavobacteriales (18%), Bacillales (7%), Pseudomonadales (11%) and members of the Alcaligenaceae family (5%) also integrated the microbial communities. An evident change had also occurred in archaeal populations at this phase. Methanosaeta became the dominant genus (95%), confirming that acetoclastic methanogenesis was the main way for methane production.
Highlights
IntroductionBeer is one of the oldest and most consumed beverages worldwide after water and tea
VFA concentrations (Table 3) never reached the inhibitory level for methanogenic activity throughout the experiment and, more importantly, the limit of propionic acid concentration was maintained lower than 2000 mg/L, as stated by Lee et al [75], not inhibiting the methanogens. These results show that communities of bacterial and archaeal populations were affected by the composition of the substrates mixture of brewery wastewater and piggery effluent, and by the Hydraulic retention times (HRT) and organic loading rates (OLR) operating conditions
The inhibiting capacity of the unusual and concentrated piggery effluent can be advantageously overcome by applying the complementary effluents concept
Summary
Beer is one of the oldest and most consumed beverages worldwide after water and tea. In Portugal, the volume of beer produced amounted to more than 6.76 million hectoliters in 2018 [1]. The production of this beverage always creates a large volume of wastewater, in addition to the water spent on washing bottles, tanks, and machines, whose discharge (3–10 L for every liter of beer) will contribute to the oxygen depletion and eutrophication of water bodies [2]. It has been estimated that 1 L of beer packaged in glass bottles consumes 17.5 MJ of primary energy and generates 842 g of CO2 eq emissions [3]
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