UASB Performance and Perspectives in Urban Wastewater Treatment at Sub-Mesophilic Operating Temperature

UASBs present several advantages compared to conventional wastewater treatment processes, including relatively low construction cost facilities, low excess sludge production, plain operation and maintenance, energy generation in the form of biogas, robustness in terms of COD removal efficiency, pH stability, and recovery time. Although anaerobic treatment is possible at every temperature, colder climates lead to lower process performance and biogas production. These factors can be critical in determining the applicability and sustainability of this technology for the treatment of urban wastewater at low operating temperature. The purpose of this study is the performance evaluation of a pilot-scale (2.75 m3) UASB reactor for treatment of urban wastewater at sub-mesophilic temperature (25 °C), below the optimal range for the process, as related to biogas production and organic matter removal. The results show that, despite lower methane production and COD removal efficiency compared to operation under ideal conditions, a UASB can still achieve satisfactory performance, and although not sufficient to grant effluent discharge requirements, it may be used as a pretreatment step for carbon removal with some degree of energy recovery. Options for UASB pretreatment applications in municipal WWTPs are discussed.

Efficiency of an up-flow Anaerobic Sludge Blanket reactor coupled with an electrochemical system to remove chloramphenicol in swine wastewater

The application and design of treatment systems in wastewater are necessary due to antibiotics' potential toxicity and resistant genes on residual effluent. This work evaluated a coupled bio-electrochemical system to reduce chloramphenicol (CAP) and chemical oxygen demand (COD) on swine wastewater (SWW). SWW characterization found CAP of <10 μg/L and 17,434 mg/L of COD. The coupled system consisted of preliminary use of an Up-flow Anaerobic Sludge Blanket Reactor (UASB) followed by electrooxidation (EO). UASB reactor (primary stage) was operated for three months at an organic load of 8.76 kg of COD/m3d and 50 mg CAP/L as initial concentration. In EO, we carried out a 22 (time operation and intensity) factorial design with a central composite design; we tried two Ti cathodes and one anode of Ti/PbO2. Optimal conditions obtained in the EO process were 240 min of operation time and 1.51 A of current intensity. It was possible to eliminate 44% of COD and 64.2% of CAP in the preliminary stage. On bio-electrochemical, a total COD and CAP removal were 82.35% and >99.99%, respectively. This coupled system can be applied to eliminate antibiotics and other organic pollutants in agricultural, industrial, municipal, and other wastewaters.

Anaerobic Degradation of Dairy Wastewater in Intermittent UASB Reactors: Influence of Effluent Recirculation

This work studied the influence of effluent recirculation upon the kinetics of anaerobic degradation of dairy wastewater in intermittent UASB (Upflow Anaerobic Sludge Bed) reactors. Several laboratory-scale tests were performed with different organic loads in a UASB reactor inoculated with flocculent sludge from an industrial wastewater treatment plant. The data obtained were used for determination of specific substrate removal rates and specific methane production rates and adjusted to kinetic models. A high initial substrate removal was observed in all tests due to adsorption of organic matter onto the anaerobic biomass which was not accompanied by biological substrate degradation as measured by methane production. Initial methane production was about 45% of initial soluble and colloidal substrate removal rate. This discrepancy was observed mainly in the first day of all experiments and was attenuated in the second day. Effluent recirculation raised significantly the rate of removal of soluble and colloidal substrate and methane productivity as compared to literature results for batch assays without recirculation.

Hydrodynamic Evaluation of Five Influent Distribution Systems in a Cylindrical UASB Reactor Using CFD Simulations

UASB reactors are a promising option for environmentally friendly wastewater treatment due to their reduced carbon footprint and their capacity to treat a variety of wastewater strengths, among other recognized advantages over alternative wastewater treatment systems. The Influent Distribution System (IDS) is a critical structure for generating granules in a UASB reactor since it provides the required flow hydrodynamics for their formation. Thus, the objective of this study was to evaluate and compare the efficiency of five IDS configurations to generate ideal granulation conditions using Computational Fluid Dynamics (CFD) simulations. The IDS configurations were as follows: (C1) single radial inflow, (C2) upward axial inflow, (C3) downward distributed axial inflow, and two novel configurations in the form of (C4) double opposite radial inflow and (C5) downward tangential inflow. The hydrodynamic response of configuration C1 was validated in a physical model with dynamic Froude similitude. The granulation measurement was velocity-based in the reactor reaction zone using steady-state CFD simulations. The novel IDS configuration C4 was the one that resulted in the highest granulation volume, with up to 45.5% of the potential granulation volume of the UASB reactor, in contrast to the IDS C2 that obtained the lowest granulation with only 10.8%. Results confirm that the IDS directly impacts the hydrodynamics of the reactor and that model-based design can be used to ascertain IDS configurations that better promote granulation in UASB reactors.

Sequential Congo Red Elimination by UASB Coupled to Electrochemical Systems

Response surface methodology was investigated to determine the operational parameters on the degradation of Congo red dye (CR) and chemical oxygen demand (COD) in two electrochemical systems evaluated individually on effluent pretreated by an up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was fed with 100 mg L−1 of CR and was operated for 12 weeks at different hydraulic residence times (HRTs) of 12 h, 10 h, and 8 h. Once stabilized at an HRT of 8 h, the effluent was collected, homogenized, and independently treated by electrooxidation (EO) and electrocoagulation (EC) cells. On both electrochemical systems, two electrode pairs were used; solid for EC (Fe and stainless-steel) and mesh electrodes for EO (Ti/PbO2 and Ti), and the effect of intensity (A), recirculation flow rate (mL min−1), and experimental time (min) was optimized on response variables. The maximum efficiencies of sequential systems for COD degradation and CR decolorization were 92.78% and 98.43% by EC and ≥99.84% and ≥99.71% by EO, respectively. Results indicate that the coupled systems can be used in textile industry wastewater treatment for the removal of dyes and the decolorized by-products.

Organic Matter Removal in a Simultaneous Nitrification-Denitrification Process Using Fixed-Film System.

This study focused on evaluating different support media for COD and nitrogen compound removal from an Upflow Anaerobic Sludge Blanket (UASB) reactor fed with swine wastewater. Maximum specific nitrification (MSNA) and denitrification (MSDA) activity tests were performed in two fixed-film systems with (1) polyurethane foam (R1) and (2) polyethylene rings (R2). The results showed that the R2 system performed more efficiently than R1, reaching organic matter removal of 77 ± 8% and nitrogen of 98 ± 4%, attributed to higher specific denitrifying activity recorded (5.3 ± 0.34 g NO3--N/g VTS ∙h). In this sense, MSDA tests indicated that the suspended biomass was responsible for at least 70% of nitrogen removal in the form of ammonium compared with 20% attributed to biomass in the form of biofilm. On the other hand, 40 ± 5% of initial nitrogen could not be quantified in the system effluents, but 10 ± 1% was attributed to loss by volatilization. According to the analyses, the previous information infers the development of simultaneous nitrification-denitrification (SND) routes. Respect to the analyses of microbial diversity and abundance in the biofilm of R2 rings, the presence of the genus Pseudomonas dominated the prokaryotic community of the system in 54.4%.

Biotransformation of congo red in a UASB reactor under salinity conditions using immobilized redox mediator in granular activated carbon

Azo dyes are susceptible to be treated by reductive biotransformation process under anaerobic conditions. The process can be accelerated by the addition of quinones and humic substances acting as redox mediators (RM). In this study, the anthraquinone-2-sulfonate (AQS) was immobilized on granular activated carbon (GAC) to evaluate the reductive biotransformation of congo red (CR) in an up-flow anaerobic sludge blanket reactor (UASB). The syudy was divided in five stages, where the reactors with immobilized RM and without RM were operated under different salinity levels (1% and 3%) and hydraulic retention times (HRT = 5 and 10 h). The reactor with immobilized RM (GAC-AQS) achieved a decolorization efficiency of 96.1% and substrate consumption of 98.8% with a HRT = 15 h and 1% of salinity. Nonetheless, with a salinity of 3% and the same HRT, the efficiency was similar (95.6%). The reactor provided with unmodified GAC achieved values below those observed in the reactor GAC-AQS, with decolorization efficiencies of 90.8% and 75.8%, and substrate consumption of 97.1% and 88.4%, for the stages IV and V, respectively. The microbial consortium sued was able to promote the biotransformation of azo dye and no inhibitory effects were identified.

Removal and Survival of Fecal Indicators in a Constructed Wetland after UASB Pre-Treatment

The experimentation plant, based on a sub-surface horizontal flow phytodepuration (SSHFP) unit with a pre-treatment by an upflow anaerobic sludge blanket (UASB) reactor, proved valuable in treating the sewage of a small rural community located in north Brazil. During a six-month trial, the plant achieved an average removal efficiency of 98.2% (1.74 log removal) for fecal coliforms (FC) and 96.0% (1.40 log removal) for Enterococci (EN), as well as 95.6% for BOD5, 91.0% for COD,00 and 95.4% for suspended solids (SS). The contribution of the UASB reactor to this overall performance was very significant as, alone, it achieved a yield of 62.7% for FC and 60% for EN, in addition to 65.2% for BOD5 and 65.0% for SS. EN was chosen, in addition to FC, because of its higher specificity and strong environmental persistence, leading to an increased risk to human health. In fact, the experimental results confirmed its lower removal efficiency compared to FC. The mechanical and biological mechanisms that led to such a removal efficiency of the two fecal indicators (FIs) are outlined in the article. The same mechanisms led to a good level of equivalence between the removal efficiency of the two FIs with the removal efficiency of SS and BOD5, for both the whole plant and the UASB reactor alone. The research demonstrated the close correlation between the concentrations of EN and FC for the plant effluent. This correlation can be explained by the following mathematical expression of the regression line Log EN = 0.2571 Log FC + 3.5301, with a coefficient of determination R2 = 0.912. This implies that the concentration of the more specific indicator EN could be calculated, with acceptable approximation, from the simple analysis of FC and vice versa. The experimental plant brought important health benefits to the local population. In particular, there were no significant odor emissions; moreover, the risk of fecal pathogenic diseases was drastically reduced; finally, there was no proliferation of insects and other disease vectors, due to the absence of stagnant or semi-stagnant water exposed to the atmosphere.