Search Results (6)

Nitrogen removal in the sewage treatment process is a significant challenge. The increase in nitrogen content in sewage leads to the eutrophication of water bodies and the deterioration of water quality in polluted environments. Therefore, converting nitrogen into non-polluting gases is a crucial and essential part of the sewage treatment process. Compared to physical, chemical, and physicochemical methods, biological denitrification is not only simple to operate and economically effective but also has less secondary pollution and saves energy. This paper summarizes the latest research progress on mainstream biological denitrification technology in WWTPS (wastewater treatment plants) and discusses its research background, methodology, and challenges. It is noted that the traditional biological nitrogen removal method is stable and widely used, but it has drawbacks such as high costs and long reaction times, especially in high-nitrogen-load wastewater treatment where its effectiveness is limited. The short-cut nitrification–denitrification process suits high-nitrogen-loading and a low C/N ratio wastewater as it reduces carbon source consumption. However, the problems of water quality fluctuation and unstable dissolved oxygen still need to be solved. The anaerobic ammonia oxidation process efficiently converts ammonia and nitrite to nitrogen using anaerobic ammonia-oxidizing bacteria, consuming less energy but facing limitations due to slow bacterial growth rates and stringent environmental conditions. The heterotrophic nitrification–aerobic denitrification process merges the traits of heterotrophic nitrifying bacteria and aerobic denitrifying bacteria, effectively reducing the ecological footprint and enhancing treatment efficiency. This approach is a pivotal focus for future research endeavors. Full article

Researchers have found that maintaining the long-term stability of nitritation becomes challenging when relying on a single inhibitor. Currently, a feasible solution to this problem is to apply two or more inhibitors to achieve the synergistic suppression of NOB. However, studies on this solution have mainly focused on mainstream wastewater, while few have focused on non-mainstream wastewater. Moreover, most of the studies relating to non-mainstream wastewater have only focused on the spontaneous achievement of nitritation within a short operation time or have described nitritation collapse. Since toilet wastewater (TW), as non-mainstream wastewater, can endogenously produce free nitrous acid (FNA) through spontaneous nitritation, an attempt was made in this study through a series of field experiments to combine another inhibitor—a low concentration of dissolved oxygen (DO) available to NOB in the inner layer of biofilm—for biofilm nitritation. Under different levels of DO in the nitritation unit, the working effect and mechanism of high FNA–low available DO dual-factor suppression in maintaining nitritation stability were investigated. The results showed that the dual-factor suppression maintained the long-term stability of TW biofilm nitritation and triggered negative feedback regulation when the nitritation was unstable. A feasible method for establishing a low level of available DO based on a normalized FNA inhibitor when the COD/TN in the nitritation unit exceeds 0.50 is possible when the influent COD/TN of the unit is over 1.57. This study aimed to construct an endogenous and unregulated synergistic suppression strategy for stabilizing nitritation in non-mainstream wastewater to support the application of efficient and sustainable N-removal technology. Full article

River water quality degradation is one of the hottest environmental issues worldwide. Therefore, monitoring water quality longitudinally and temporally is crucial for effective water management and contamination control. The main aim of this study was to assess the longitudinal variations in water quality in the mainstream of the Han River, Korea, from 2015 to 2019. The trophic state classification (TSC), microbial pollution indicator (MPI), and river pollution index (RPI) were calculated to characterize river water quality and revealed more serious pollution toward the downstream zone (Dz) due to agricultural and urban-dominated areas. The biodegradability index (BI) indicated that non-biodegradable organic pollutants are increasing in the water body from the urban and animal wastewater treatment plants. Nutrients, organic matter contents, total suspended solids, ionic factors, and algal chlorophyll were higher in the Dz than in any other zones and were markedly influenced by the summer monsoon. Empirical analysis showed that nutrients and organic matter had positive linear functional relations with agricultural and urban coverage and negative linear relations with forest coverage. The pollutant-transport function suggested that suspended solids act as TP and TN carriers. Regression analysis indicated that TP (R² = 0.47) has more positive functional relations with algal growth than TN (R² = 0.22). Our findings suggest that a combination of empirical models and pollution indices might be utilized to assess river water quality and that the resulting information could aid policymakers in managing the Han River. Full article

Development and adoption of more efficient and robust technologies for reuse of wastewater embedded resources, in particular materials and energy, is becoming an unavoidable necessity. Among many emerging technologies in the sector of wastewater treatment residuals valorization, Pulsed Electric Field (PEF) processes have shown interesting potential, although they have not yet entered the sector’s mainstream as a consolidated commercial technology, as in other industrial applications, such as the food, medical, and bio-based industries. PEF is a non-thermal technology suitable to biological applications, involving gentle cell disintegration and enhanced cell membrane permeability and as such applicable to disinfection, sterilization, and to those processes that benefit from an enhanced extraction of organic compounds from biological matter, such as anaerobic digestion, biological processes for recovery of nutrients, and biorefinery of cell-embedded compounds. PEF technology applications in wastewater/biomass residues management are reported and advantages, drawbacks, and barriers of the technology are discussed in this paper. Full article

The objective of this work was to demonstrate the removal of the phosphorus and carbon dioxide capture potential of a conventional septic system upgraded with a sidestream steel slag filter used in recirculation mode. A pilot scale sidestream experiment was conducted with two septic tank and drainfield systems, one with and one without a sidestream slag filter. The experimental system was fed with real domestic wastewater. Recirculation ratios of 25%, 50% and 75% were tested. Limestone soils and non-calcareous soils were used as drainfield media. The tested system achieved a satisfactory compromise between phosphorus removal and pH at the effluent of the septic tank, thus eliminating the need for a neutralization step. The phosphorus removal efficiency observed in the second compartment of the septic tank was 30% in the slag filter upgraded system, compared to −3% in the control system. The slag filter reached a phosphorus retention of 105 mg/kg. The drainfield of non-calcareous soils achieved very high phosphorus removal in both control and upgraded systems. In the drainfield of limestone soil, the slag filtration reduced the groundwater phosphorus contamination load by up to 75%. The removal of chemical oxygen demand of the drainfields was not affected by the pH rise induced by the slag filter. Phosphorus removal in the septic tank with a slag filter was attributed to either sorption on newly precipitated calcium carbonate, or the precipitation of phosphate minerals, or both. Recirculation ratio design criteria were proposed based on simulations. Simulations showed that the steel slag filter partly inhibited the biological production of carbon dioxide in the septic tank. The influent alkalinity strongly influenced the recirculation ratio needed to raise the pH in the septic tank. The recirculation mode allowed clogging mitigation compared to a mainstream configuration, because an important part of chemical precipitation occurred in the septic tank. The control septic tank produced carbon dioxide, whereas the slag filter-upgraded septic tank was a carbon dioxide sink. Full article

A one-stage partial nitritation/anammox (PN/A) process with intermittent aeration is possible under sidestream conditions, but implementation in a mainstream is a challenge due to increased Carbon/Nitrogen (C/N) ratios in domestic wastewater. This study investigated the effect of C/N ratios on process efficiency and the effect of narrowing non-aeration time on process improvement at high chemical oxygen demand (COD) load. An increase in TN removal efficiency was achieved in both series with gradual change of C/N ratio from 1 to 3, from 65.1% to 83.4% and 63.5% to 78% in 1st and 2nd series, respectively. However, at the same time, the ammonium utilization rate (AUR) value decreased with the increase in C/N ratio. At a high COD (C/N = 3) concentration, the process broke down and regained productivity after narrowing the non-aeration time in both series. Shifts in the system performance were also connected to adaptive changes in microbial community revealed by data obtained from 16S rRNA NGS (next-generation sequencing), which showed intensive growth of the bacteria with dominant heterotrophic metabolism and the decreasing ratio of autotrophic bacteria. The study shows that deammonification is applicable to the mainstream provided that the C/N ratio and the aeration/non-aeration time are optimized. Full article