Effect of non‐feeding period length on the intermittent operation of UASB reactors treating dairy effluents

Abstract

Recent environmental concerns have prompted a re-evaluation of conventional management strategies and refueled the search of innovative waste management practices. In this sense, the anaerobic digestion of both fat and the remaining complex organic matter present in dairy wastewaters is attractive, although the continuous operation of high rate anaerobic processes treating this type of wastewaters causes the failure of the process. This work accesses the influence of non-feeding period length on the intermittent operation of mesophilic UASB reactors treating dairy wastewater, in order to allow the biological degradation to catch up with adsorption phenomenon. During the experiments, two UASB reactors were subject to three organic loading rates, ranging from 6 to 12 g(COD) x L(-1) x d(-1), with the same daily load applied to both reactors, each one with a different non-feeding period. Both reactors showed good COD removal efficiencies (87-92%). A material balance for COD in the reactors during the feeding and non-feeding periods showed the importance of the feedless period, which allowed the biomass to degrade substrate that was accumulated during the feeding period. The reactor with the longest non-feeding period had a better performance, which resulted in a higher methane production and adsorption capacity for the same organic load applied with a consequent less accumulation of substrate into the biomass. In addition, both reactors had a stable operation for the organic load of 12 g(COD) x L(-1) x d(-1), which is higher than the maximum applicable load reported in literature for continuous systems (3-6 g(COD) x L(-1) x d(-1)).

Anaerobic degradation of dairy wastewater in intermittent UASB reactors: influence of effluent recirculation

“…The results obtained in this work also suggest that for organic loads above 10 g COD L −1 , the feedless periods of intermittent operation should be longer than the feed periods as has been suggested by Coelho et al [29] On the other hand, in this work, it was confirmed that the monitoring of high-rate reactors treating complex fat containing wastewater based on the monitoring of the COD of the produced effluent may be misleading in what concerns the real biological degradation as stated by Nadais et al [22] and by Jeganathan et al [25]. This is because the difference between the feed COD and the effluent COD may not express the degradation of the substrate since accumulation may frequently occur in the sludge bed.…”

“…For a load rate of 5 kg COD m −3 d −1 , the authors observed fats accumulation in the sludge bed and scum formation, resulting in biodegradation below 50%. As an option to overcome operating problems verified in continuous systems, [25][26][27][28] studies have been developed on the intermittent operation of UASB reactors used for treating dairy wastewater [27,29] or for treating proteinaceous wastewater, [30] slaughterhouse wastewater, [31] domestic wastewater [32] or olive mill wastewater. [33] The beneficial effects of discontinuous feeding of fatty substrates on anaerobic systems have also been confirmed by Palatsi et al [34] and some results obtained in a full-scale reactor are presented by Passeggi et al [19] with effluent recirculation during the feedless phase.…”

“…The feedless period is crucial for the degradation of the complex substrates (fats and LCFA) that accumulate in the biomass during the feed period, mainly by adsorption mechanisms. [22,27,29,33] During the feed periods, the intermittent UASB reactor operates as a continuous reactor and during the feedless periods, it works as a batch reactor. It has been suggested that effluent recirculation during the feedless periods of intermittent operation was beneficial for reactor performance, especially in terms of methane production.…”

Anaerobic removal of 1-methoxy-2-propanol under ambient temperature in an EGSB reactor

“…However, studies carried out by Coelho et al [16] demonstrated that mesophilic UASB reactors operated with intermittent substrate supply treating dairy wastewater could improve biological conversion and enhance methane production in comparison with UASB reactors operated with continuous substrate supply.…”

Anaerobic co‐digestion of waste yeast biomass from citric acid production and waste frying fat

“…In contrast, Coelho et al. tested various operational conditions with a 6 h feeding time followed by a 6 h non‐feeding time and a 3 h feeding time followed by a 9 h non‐feeding time, with variable feeding flows for each case. The authors stated that an intermittent mode of feeding with longer feeding intermissions was more favorable for anaerobic digestion of fat containing substrates as the non‐feeding periods allow the biomass to degrade the substrate adsorbed into the biomass during the feeding period.…”