Removal of Emerging Contaminants from Wastewater Streams Using Membrane Bioreactors: A Review

Water is a very valuable natural resource. As the demand for water increases the presence of emerging contaminants in wastewater has become a growing concern. This is particularly true when one considers direct reuse of wastewater. Obtaining sufficient removal of emerging contaminants will require determining the level of removal for the various unit operations in the wastewater treatment process. Membrane bioreactors are attractive as they combine an activated sludge process with a membrane separation step. They are frequently used in a wastewater treatment process and can operate at higher solid loadings than conventional activated sludge processes. Determining the level of removal of emerging contaminants in the membrane bioreactor step is, therefore, of great interest. Removal of emerging contaminants could be by adsorption onto the biomass or membrane surface, biotransformation, size exclusion by the membrane, or volatilization. Given the fact that most emerging contaminants are low molecule weight non-volatile compounds, the latter two methods of removal are usually unimportant. However, biotransformation and adsorption onto the biomass are important mechanisms of removal. It will be important to determine if the microorganisms present at given treatment facility are able to remove ECs present in the wastewater.

Simulation of an Oxic-Settling-Anaerobic Pilot Plant Operated under Real Conditions Using the Activated Sludge Model No.2d

Oxic-settling-anaerobic (OSA) process has been introduced into the treatment line of wastewater in order to upgrade activated sludge processes and to reduce the production of excess sludge. The aim of the present study was to simulate the performance of an OSA pilot plant by implementing the Activated Sludge Model No.2d (ASM2d) into a mathematical modelling software (BioWin). The stepwise calibration, performed both by off-line experiments and software dynamic calibration, was carried out in a heuristic way, adjusting the parameters values that showed a major influence to the effluent and internal concentrations. All the reduction factors introduced into ASM2d to simulate the processes occurring in anoxic and anaerobic conditions were lowered in order to reproduce the concentrations of interest. In addition, the values of parameters of the PAOs (polyphosphate accumulating organisms)-related process (namely qPHA and YPO4) were found lower than those usually adopted. In general, theoretical results were in good agreement with the experimental data obtained from plant’s operation, showing an accurate predictive capacity of the model. Good performance was achieved considering the phosphorus removal related process, while some failures were detected in COD and ammonia simulations.

Oxygen requirements in relation to sludge age in wastewater treatment plants

Sustainability of activated sludge (AS) wastewater treatment processes is inexplicably linked to minimization of secondary wastes, such as waste sludge, as well as energy requirements for achieving effluent quality standards. Oxygen requirements and waste sludge management accounts for most of energy consumption in aerobic AS wastewater treatment plants (WWTPs). In this study, a novel, highly aerobic AS process, entitled complete solids retention AS process (CRAS), is being evaluated in terms of waste sludge production and biomass oxygen utilization rate. Aim of this work is to study the effect of solids retention time (SRT) on observed sludge yields and on oxygen requirements for respiration in order to evaluate CRAS process as a sustainable alternative to typical activated sludge processes.

Recovery of Biodegradable Bioplastics from Different Activated Sludge Processes during Wastewater Treatment

To overcome the environmental hazards of petroleum based plastics, synthesis and use of microbial bioplastics became popular. Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers having plastic like properties mainly used in tissue engineering and packaging. Bacteria can produce bioplastics in carbon abundance. Activated sludge process is a simultaneous process for treating wastewater and producing PHAs. Wastewaters are treated by using mixed sludge, aerobic granular sludge and chemically treated sludge which provided more than 40% PHA yield. This chapter describes the PHA structure, synthesis pathways, types of wastewaters and activated sludge processes used with reactor parameters and environmental factors effecting PHA productions.

Combination of sonophotolysis and aerobic activated sludge processes for treatment of synthetic pharmaceutical wastewater.

The treatment ability and efficiency of sonophotolytic process, aerobic activated sludge (AS) process, and their combination in reduction of total organic carbon (TOC), total nitrogen (TN), chemical oxygen demand (COD), and biological oxygen demand (BOD) from a synthetic pharmaceutical wastewater (SPWW) were studied. Batch mode experiments were performed to obtain optimal experimental operating conditions for sonophotolysis process. Ultrasonic power of 140 W, initial pH solution of 2, and air flow rate of 3 L/min were found as optimum. The initial optimum molar ratio of H2O2/TOC was found to be 13.77 for sonophotolysis process alone in batch mode. In continuous mode, sonophotolysis was able to reduce TOC by 90% after 180 min retention time. Aerobic AS process alone after 48 h retention time reduced TOC by 67%. Combined sonophotolysis and aerobic AS processes improved the biodegradability of the SPWW and resulted in 98% TOC and 99% COD removal while decreasing the retention time in sonophotoreactor and aerobic AS reactor to 120 min and 24 h, respectively. Additionally, the consumption of H2O2 was reduced significantly in the combined processes.

Combination of sonophotolysis and aerobic activated sludge processes for treatment of synthetic pharmaceutical wastewater.

The treatment ability and efficiency of sonophotolytic process, aerobic activated sludge (AS) process, and their combination in reduction of total organic carbon (TOC), total nitrogen (TN), chemical oxygen demand (COD), and biological oxygen demand (BOD) from a synthetic pharmaceutical wastewater (SPWW) were studied. Batch mode experiments were performed to obtain optimal experimental operating conditions for sonophotolysis process. Ultrasonic power of 140 W, initial pH solution of 2, and air flow rate of 3 L/min were found as optimum. The initial optimum molar ratio of H2O2/TOC was found to be 13.77 for sonophotolysis process alone in batch mode. In continuous mode, sonophotolysis was able to reduce TOC by 90% after 180 min retention time. Aerobic AS process alone after 48 h retention time reduced TOC by 67%. Combined sonophotolysis and aerobic AS processes improved the biodegradability of the SPWW and resulted in 98% TOC and 99% COD removal while decreasing the retention time in sonophotoreactor and aerobic AS reactor to 120 min and 24 h, respectively. Additionally, the consumption of H2O2 was reduced significantly in the combined processes.

Unwanted mainstream nitritation-denitritation causing massive N2O emissions in a continuous activated sludge process

Nitrous oxide emissions can contribute significantly to the carbon footprint of municipal wastewater treatment plants even though emissions from conventional nitrogen removal processes are assumed to be moderate. An increased risk for high emissions can occur in connection with process disturbances and nitrite (NO2−) accumulation. This work describes the findings at a large municipal wastewater treatment plant where the levels of NO2− in the activated sludge process effluent were spontaneously and strongly increased on several activated sludge lines which was suspected to be due to shortcut nitrogen removal that stabilized for several months. The high NO2− levels were linked to a dramatic increase in nitrous oxide (N2O) emissions. As much as over 20% of the daily influent nitrogen load was emitted as N2O. These observations indicate that highly increased NO2− levels can occur in conventional activated sludge processes and result in high nitrous oxide emissions. They also raise questions concerning the risk of increased greenhouse gas (GHG) emissions of the nitritation-denitritation processes – although the uncontrolled nature of the event described here must be taken into consideration – and underline the importance of continuous monitoring and control of N2O emissions.

The Sensitivity of a Specific Denitrification Rate under the Dissolved Oxygen Pressure

The biological denitrification process is extensively discussed in scientific literature. The process requires anoxic conditions, but the influence of residual dissolved oxygen (DO) on the efficiency is not yet adequately documented. The present research aims to fill this gap by highlighting the effects of DO on the specific denitrification rate (SDNR) and consequently on the efficiency of the process. SDNR at a temperature of 20 °C (SDNR20°C) is the parameter normally used for the sizing of the denitrification reactor in biological-activated sludge processes. A sensitivity analysis of SNDR20°C to DO variations is developed. For this purpose, two of the main empirical models illustrated in the scientific literature are taken into consideration, with the addition of a deterministic third model proposed by the authors and validated by recent experimentations on several full-scale plants. In the first two models, SDNR20°C is expressed as a function of the only variable food:microrganism ratio in denitrification (F:MDEN), while in the third one, the dependence on DO is made explicit. The sensitivity analysis highlights all the significant dependence of SDNR20°C on DO characterized by a logarithmic decrease with a very pronounced gradient in correspondence with low DO concentrations. Moreover, the analysis demonstrates the relatively small influence of F:MDEN on the SDNR20°C and on the correlation between SDNR20°C and DO. The results confirm the great importance of minimizing DO and limiting, as much as possible, the transport of oxygen in the denitrification reactor through the incoming flows and mainly the mixed liquor recycle. Solutions to achieve this result in full-scale plants are reported.