NH4+ ad-/desorption in sequencing batch reactors: simulation, laboratory and full-scale studies

Development and application of random forest regression soft sensor model for treating domestic wastewater in a sequencing batch reactor

Small-scale distributed water treatment equipment such as sequencing batch reactor (SBR) is widely used in the field of rural domestic sewage treatment because of its advantages of rapid installation and construction, low operation cost and strong adaptability. However, due to the characteristics of non-linearity and hysteresis in SBR process, it is difficult to construct the simulation model of wastewater treatment. In this study, a methodology was developed using artificial intelligence and automatic control system that can save energy corresponding to reduce carbon emissions. The methodology leverages random forest model to determine a suitable soft sensor for the prediction of COD trends. This study uses pH and temperature sensors as premises for COD sensors. In the proposed method, data were pre-processed into 12 input variables and top 7 variables were selected as the variables of the optimized model. Cycle ended by the artificial intelligence and automatic control system instead of by fixed time control that was an uncontrolled scenario. In 12 test cases, percentage of COD removal is about 91. 075% while 24. 25% time or energy was saved from an average perspective. This proposed soft sensor selection methodology can be applied in field of rural domestic sewage treatment with advantages of time and energy saving. Time-saving results in increasing treatment capacity and energy-saving represents low carbon technology. The proposed methodology provides a framework for investigating ways to reduce costs associated with data collection by replacing costly and unreliable sensors with affordable and reliable alternatives. By adopting this approach, energy conservation can be maintained while meeting emission standards.

Sequencing batch reactor technology for landfill leachate treatment: A state-of-the-art review

Landfill has become an underlying source of surface and groundwater pollution if not efficiently managed, due to the risk of leachate infiltration into to land and aquifers. The generated leachate is considered a serious environmental threat for the public health, because of the toxic and recalcitrant nature of its constituents. Thus, it must be collected and appropriately treated before being discharged into the environment. At present, there is no single unit process available for proper leachate treatment as conventional wastewater treatment processes cannot achieve a satisfactory level for degrading toxic substances present. Therefore, there is a growing interest in examination of different leachate treatment processes for maximum operational flexibility. Based on leachate characteristics, discharge requirements, technical possibilities, regulatory requirements and financial considerations, several techniques have been applied for its degradation, presenting varying degrees of efficiency. Therefore, this article presents a comprehensive review of existing research articles on the pros and cons of various leachate degradation methods. In line with environmental sustainability, the article stressed on the application and efficiency of sequencing batch reactor (SBR) system treating landfill leachate due to its operational flexibility, resistance to shock loads and high biomass retention. Contributions of integrated leachate treatment technologies with SBR were also discussed. The article further analyzed the effect of different adopted materials, processes, strategies and configurations on leachate treatment. Environmental and operational parameters that affect SBR system were critically discussed. It is believed that information contained in this review will increase readers fundamental knowledge, guide future researchers and be incorporated into future works on experimentally-based SBR studies for leachate treatment.

pH dependent of the waste activated sludge reduction by short-time aerobic digestion (STAD) process

The short-time aerobic digestion (STAD) process has been found to be a unique and significant technique for the stabilization of waste activated sludge (WAS), but the influences of the system pH on the STAD process was unclear. This study systematically disclosed the influences of the system pH on the STAD process of WAS. Under neutral or weak alkaline conditions, although the biodegradation rates of VSS (~0.0085 h^-1) were low, high biodegradation rates of TCOD (k_TCOD) (~0.0096 h^-1) were achieved. Less releases of the biopolymers from the WAS led to low concentrations of STOC, UV₂₅₄, the low MW organic matters, NH₄⁺ - N and PO₄^3- - P in the supernatant. However, the appropriate pH for the microorganisms improved SOUR, indicating that the released substances were further reused or biodegraded by the microorganisms. Under acidic or alkaline conditions, the biodegradation rates of VSS (0.009-0.019 h^-1) and TCOD (k_TCOD) (0.005-0.009 h^-1) were opposite with those under neutral or weak alkaline conditions. The releases of the biopolymers were increased, leading to high concentrations of STOC, UV₂₅₄, the low MW organic matters, PO₄^3- - P and NH₄⁺ - N in the supernatant. However, the extreme pH inhibited the microbial activity. The SOURs were only 0.0097 h^-1 and 0.0053 h^-1 for system pH of 8.0 and 4.0, respectively. Accordingly, neutral and weak alkaline conditions should be more suitable for the STAD process of WAS. This work lays the foundation for optimizing system pH for the reduction of WAS in STAD system.

The characteristics of heat-driven ammonium adsorption in aerobic granular sludge

Adsorption is an important step during the migration of ammonium from the aqueous phase to biomass in biological nitrogen removal processes. A deeper understanding of the adsorption mechanisms is encouraged in constructing nitrogen conversion models. In this study, the ammonium adsorption in aerobic granular sludge was investigated at different conditions. Analysis of kinetic data indicated that ammonium adsorption was a fast process and followed pseudo-second-order kinetics (adsorption rate constant k₂ was between 0.031 and 0.065 g/(mg · min)). The maximum adsorption capacity and half saturation constant K_L in the Langmuir isotherm model were 4.95 mgNH₄ ⁺-N/g total suspended solids and 0.0126 L/mg, respectively. Effects of environmental conditions such as temperature, pH and competitive cations were also estimated. The optimum pH was 7 and the effects of competitive cations were in the order Ca²⁺ > Mg²⁺ > K⁺ > Na⁺. Values of thermodynamic parameters (ΔH^Ɵ = -14.697 kJ/mol, ΔS^Ɵ = -6.65 J/(mol · K)) indicated that the adsorption process was spontaneous and exothermic. Desorption tests showed that the process was reversible and low temperature had a negative effect on ammonium desorption. These findings could be useful for completing the mathematical model of the nitrogen removal process in bioreactors.

Insight into the roles of tightly and loosely bound extracellular polymeric substances on a granular sludge in ammonium nitrogen removal

To explicitly understand the function of extracellular polymeric substances in the treatment of ammonium-nitrogen-rich wastewater using aerobic granular sludge, the three forms of nitrogen (ammonium, nitrite and nitrate nitrogen) contained in tightly and loosely bound extracellular polymeric substances were analyzed. The three forms of nitrogen were monitored in the tightly and loosely bound extracellular polymeric substances in aerobic granular sludge after adsorption. The ammonium nitrogen contained in the extracellular polymeric substances was distributed in both the tightly and loosely bound forms and decreased gradually as the aeration time increased. Ammonium nitrogen remained in the tightly bound extracellular polymeric substances even after aeration was complete. The nitrite and nitrate nitrogen species in the extracellular polymeric substances were mainly present in the loosely bound extracellular polymeric substances. The sources of the three nitrogen forms detected in the extracellular polymeric substances differed relative to the different nitrogen forms.

Simultaneous nitrification and denitrification by EPSs in aerobic granular sludge enhanced nitrogen removal of ammonium-nitrogen-rich wastewater

In this study, role of extracellular polymeric substances (EPSs) in enhancing nitrogen-removal from ammonium-nitrogen-rich wastewater using aerobic granular sludge (AGS) technology were analyzed. AGS enabled ammonium oxidation and denitrification to occur simultaneously. Air stripping and simultaneous nitrification-denitrification contributed to total-nitrogen removal. Clone-library analysis revealed that close relatives of Nitrosomonas eutropha and heterotrophic denitrifiers were dominant in the AGS, whereas anammox bacteria were not detected. EPSs adsorption of ammonium, nitrite, and nitrate nitrogen results in improved removal of nitrogen in batch experiments.

The contribution of exopolysaccharides induced struvites accumulation to ammonium adsorption in aerobic granular sludge

Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH4+-N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides.

Ammonium adsorption in aerobic granular sludge, activated sludge and anammox granules

The ammonium adsorption properties of aerobic granular sludge, activated sludge and anammox granules have been investigated. During operation of a pilot-scale aerobic granular sludge reactor, a positive relation between the influent ammonium concentration and the ammonium adsorbed was observed. Aerobic granular sludge exhibited much higher adsorption capacity compared to activated sludge and anammox granules. At an equilibrium ammonium concentration of 30 mg N/L, adsorption obtained with activated sludge and anammox granules was around 0.2 mg NH4-N/g VSS, while aerobic granular sludge from lab- and pilot-scale exhibited an adsorption of 1.7 and 0.9 mg NH4-N/g VSS, respectively. No difference in the ammonium adsorption was observed in lab-scale reactors operated at different temperatures (20 and 30 °C). In a lab-scale reactor fed with saline wastewater, we observed that the amount of ammonium adsorbed considerably decreased when the salt concentration increased. The results indicate that adsorption or better ion exchange of ammonium should be incorporated into models for nitrification/denitrification, certainly when aerobic granular sludge is used.