Increasing salinity concentrations determine the long-term participation of methanogenesis and sulfidogenesis in the biodigestion of sulfate-rich wastewater.

The competition between sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) depends on several factors, such as the COD/SO42- ratio, sensitivity to inhibitors and even the length of the operating period in reactors. Among the inhibitors, salinity, a characteristic common to diverse types of industrial effluents, can act as an important factor. This work aimed to evaluate the long-term participation of sulfidogenesis and methanogenesis in the sulfate-rich wastewater process (COD/SO42- = 1.6) in an anaerobic structured-bed reactor (AnSTBR) using sludge not adapted to salinity. The AnSTBR was operated for 580 d under mesophilic temperature (30 °C). Salinity levels were gradually increased from 1.7 to 50 g-NaCl L-1. Up to 35 g-NaCl L-1, MA and SRB equally participated in COD conversion, with a slight predominance of the latter (53 ± 11%). A decrease in COD removal efficiency associated with acetate accumulation was further observed when applying 50 g-NaCl L-1. The sulfidogenic pathway corresponded to 62 ± 17% in this case, indicating the inhibition of MA. Overall, sulfidogenic activity was less sensitive (25%-inhibition) to high salinity levels compared to methanogenesis (100%-inhibition considering the methane yield). The wide spectrum of SRB populations at different salinity levels, namely, the prevalence of Desulfovibrio sp. up to 35 g-NaCl L-1 and the additional participation of the genera Desulfobacca, Desulfatirhabdium, and Desulfotomaculum at 50 g-NaCl-1 explain such patterns. Conversely, the persistence of Methanosaeta genus was not sufficient to sustain methane production. Hence, exploiting SRB populations is imperative to anaerobically remediating saline wastewaters.

Evaluation of sulfamethazine removal kinetics using fixed structured bed bioreactor.

The use of anaerobic biomass attached to a support has been recently presented as a good prospect in the treatment of wastewater containing recalcitrant compounds, such as sulfamethazine (SMZ). SMZ has been found in swine wastewater and sewage treatment plants, which motivates assessing their degradation by new wastewater treatment technologies. Thus, this paper describes the use of a continuous fixed structured bed bioreactor for the purpose of evaluating SMZ removal kinetics present in lab-made wastewater. The analysis of SMZ used online solid-phase extraction coupled to liquid chromatography/tandem mass spectrometry (SPE online-LC-MS/MS). Chemical oxygen demand (COD) was also monitored to evaluate the organic matter removal. The bioreactor was operated under mesophilic conditions (30 ∘ C), with a hydraulic retention time of 24 h. In order to evaluate SMZ removal, four different concentration levels were studied: 200, 400, 600, and 800 ng L-1. COD removal efficiency obtained for filtered effluent kept at 91.01% and there was no interference due to the increase of SMZ concentration. For SMZ, the removal efficiencies were of 52.8±12.1% for 200 ng L-1 concentration level; 55.0±8.15% for 400 ng L-1; 53.0±6.14% for 600 ng L-1, and 48.8±5.44% for 800 ng L-1. COD removal kinetics presented a first-order apparent removal rate constant ( kapp ) of 0.281±0.0295 h-1. SMZ also showed a first-order apparent removal rate constant of 0.158±0.0093 h-1 for the following concentrations levels: 200, 400, 600, and 800 ng L-1.

Removal kinetics of sulfamethazine and its transformation products formed during treatment using a horizontal flow-anaerobic immobilized biomass bioreactor.

Sulfamethazine (SMZ) is an antibiotic from sulfonamides class widely used in veterinary medicine and reported in wastewater and sewage. Thus, it is essential to study technologies to reduce SMZ present in the aquatic environment. Anaerobic bioreactors are a low-cost technology applied for wastewater treatment. The objective of this paper is to study kinetics parameters related to SMZ removal using a horizontal flow-anaerobic immobilized biomass reactor (HAIB) and to evaluate its transformation products formed during this treatment. The bioreactor was operated at mesophilic condition with a hydraulic retention time of 12 h. The removal of SMZ was evaluated at three different concentrations: 200 ng L-1 (phase I), 400 ng l-1 (phase II) and 600 ng L-1 (phase III). The apparent first-order removal constant obtained for chemical oxygen demand was 0.885 ± 0.094 h-1 while SMZ showed a removal constant of 0.356 h-1. SMZ was removed with an efficiency of 56.0 ± 13.0 % (phase I); 62.0 ± 12.0 % (phase II) and 62.0 ± 6.00 % (phase III). Seven transformation products were detected and one of these with m/z 233 is reported for the first-time. The HAIB bioreactor has a potential to assist in wastewater treatment to remove contaminants at ng L-1 concentration level.