Optimizing and real-time control of biofilm formation, growth and renewal in denitrifying biofilter

Achieving mainstream anammox in biological aerated filter by regulating bacteria community structure

Although mainstream partial nitrification-anammox (PN-A) is a highly efficient and sustainable wastewater treatment process, it is difficult to achieve and stabilize due to the competition among functional bacteria. In this study, achieving one-stage mainstream anammox via regulating bacteria community structure was studied in a lab-scale biological aerated filter (BAF). The results showed that high free ammonia with 89.57 mg/L, nitrite nitrogen (NO₂^--N) competition between anammox bacteria (AnAOB) and nitrite oxidizing bacteria (NOB), and backwash regulated the bacteria community structure. After backwash, Candidatus Kuenenia became the dominant bacteria and the relative abundance increased to 5.56 %. In BAF, one-stage mainstream anammox with total nitrogen (TN) being lower than 15 mg/L in the effluent was achieved using lag-time of bacteria activity recovery caused by alternating operation of high and low ammonia nitrogen (NH₄⁺-N), which have great potential applied in municipal wastewater treatment plants (MWWTPs).

Influence mechanism of filling ratio on solid-phase denitrification with polycaprolactone as biofilm carrier

In this study, three up-flow fixed-bed bioreactors were constructed with three different filling ratios (filling volume/effective volume: 30%, 60% and 90%) of polycaprolactone (PCL). Above 98% of nitrate removal efficiency was achieved with low accumulations of nitrite and ammonium for each filling ratio. Low filling ratio of PCL had extensive folds and pores that favored the attachment and growth of microorganisms; however, excessive biomass restrained nitrate specific reduction rate (NaSRR). The most dominant genera were Comamonas (0.80-57.64%), Stenotrophomonas (2.59-54.39%), Acidovorax (7.32-23.55%), Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium (0.30-19.74%) and Thermomonas (0.12-14.58%). Nitrate reductase (EC 1.7.99.4), nitrite reductase (EC 1.7.2.1) and nitric oxide reductase (EC 1.7.2.5) predicted by PICRUSt2 were abundant in high influent nitrate load (NaL). According to the analysis of carbon balance model, the utilization rate (η) of PCL showed a highly positive correlation with influent NaL, indicating reducing filling ratio or HRT might be an effective measure to save cost for nitrate removal.

Effect of filling ratio and backwash on performance of a continuous-flow SPD reactor packed with PCL as carbon source

In this study, three up-flow fixed-bed bioreactors, named as A, B, and C, packed with polycaprolactone (PCL) under different filling ratios (31%, 62%, and 93%, respectively), were investigated over a long period (96 days). During the stable period, the mean effluent NO 3 - - N concentrations in reactors A, B, and C were 1.35 ± 0.50, 1.07 ± 0.41, and 1.03 ± 0.27 mg/L, respectively, which showed the removal of NO 3 - - N was not closely related to filling ratio (p > 0.05, one-way ANOVA). However, it was found that biomass in reactor A was 2.13 and 5.55 times in B and C, respectively. Excessively thick biofilm refrained the enzymatic hydrolysis of PCL and biofilm's specific denitrification rate (SDNR). Backwash stimulated organic matter release and enabled biofilm to restore its denitrification activity. The maximum cycle of backwash was 6 days for the lowest filling ratio reactor. Additionally, the utilization rates for denitrification were 83.3%, 86.4%, and 60.5% in reactors A, B, and C, respectively, which was higher after backwash than before backwash. PRACTITIONER POINTS: Excessively thick biofilm refrained the enzymatic hydrolysis of PCL. Backwash stimulated organic matter release and enabled biofilm to restore its denitrification activity. The maximum cycle of backwash was 6 days for the lowest filling ratio reactor. A higher utilization rate of PCL for denitrification was observed after backwash.

Achieving partial denitrification-anammox in biofilter for advanced wastewater treatment

Recently, partial denitrification (PDN) - anaerobic ammonium oxidation (anammox) process has been widely studied in activated sludge for nitrate wastewater treatment. However, achieving PDN-Anammox in biofilter for domestic wastewater treatment was never reported. In this study, two lab-scale PDN biofilter and Anammox biofilter were built up to treat simulated domestic wastewater. The results showed that stable nitrogen removal performance was kept with averaged effluent nitrogen of 10.2 mg/L. Stable nitrite accumulation performance was achieved with low abundance of nitrite reductase gene, while influent composition influenced nitrogen transformation pathway in PDN biofilter. When treating domestic wastewater, nitrification and partial denitrification led to the higher nitrite accumulation ratio of 75.4%. The percentage contribution of anammox biofilter was 74.6% for nitrogen removal, and Candidatus Brocadia was dominant genus. After long-term operation, limited substrate concentration caused interspecific competition among various anammox bacteria, leading to an increasing proportion of Candidatus Brocadia fulgida. PDN-Anammox biofilter is a feasible process to advanced wastewater treatment, which could save aeration consumption and carbon source addition, and reduce sludge production.

Improving nitrogen removal in biological aeration filter for domestic sewage treatment via adjusting microbial community structure

The rapid growth of nitrite-oxidizing bacteria (NOB) in reactor prevents the application of anaerobic ammonium oxidation (anammox) technology to main-stream wastewater treatment. How to eliminate NOB and reserve anaerobic ammonium oxidation bacteria (AnAOB) simultaneously becomes the biggest challenge. In this study two coupled biological aeration filters (BAFs) were built up to treat domestic sewage. In BAF1 nitrogen removal concentration was 21.4 mg/L via heterotrophic denitrification pathway. Backwash was conducted to BAF2 to improve nitrogen removal performance. After backwash Nitrospira proportion declined from 10.8% to 2.1%, while Candidatus Kuenenia percentage increased from 5.6% to 10.2%. Nitrogen removal concentration improved from 8.6 mg/L to 22.8 mg/L via anammox pathway in BAF2, and total nitrogen removal concentration reached to 44.2 mg/L in two coupled BAFs during aeration process. These findings could provide a new strategy for the application of anammox technology to main-stream wastewater treatment.

Removal Characteristics of Dissolved Organic Nitrogen and Its Bioavailable Portion in a Postdenitrifying Biofilter: Effect of the C/N Ratio

Addition of external carbon sources to postdenitrification biofilters (DNFs) is frequently used in municipal wastewater treatment plants to enhance dissolved inorganic nitrogen removal. However, little is known about its influence on the removal of dissolved organic nitrogen (DON). This study investigated the effect of the carbon-to-nitrogen (C/N) ratio (3, 4, 5, and 6) on the removal characteristics of DON and bioavailable DON (ABDON) in the pilot-scale DNFs treating real secondary effluent. Results showed that DNFs effluent DON accounted for 31.2-39.8% of the effluent total nitrogen. The maximum effluent DON and ABDON concentrations both occurred in DNF operated at a C/N ratio of 3. There was no significant difference in effluent DON concentrations in DNFs at C/N ratios of 4, 5, and 6; however, effluent ABDON and DON bioavailability significantly decreased with C/N ratios (p < 0.05, t-test). According to the chemical composition analysis, effluent DON at high C/N ratios tends to contain less % molecular weight < 1 kDa nitrogenous organic compounds and proteins/amino sugars-like nitrogenous organic formulas, which is likely responsible for its low bioavailability. Overall, this study indicates the benefit of a high C/N ratio during the DNF process in terms of controlling the DON forms that readily stimulate algal growth.

Nitrate removal, spatiotemporal communities of denitrifiers and the importance of their genetic potential for denitrification in novel denitrifying bioreactors

Nitrate treatment performance and denitrification activity were compared between denitrifying biological filters (DNBFs) based on dewatered alum sludge (DAS) and neutralized used acid (NUA). The spatiotemporal distribution of denitrifying genes and the genetic potential associated with denitrification activity and nitrate removal in both DNBFs were also evaluated. The removal efficiency of NUA-DNBF increased by 8% compared with that of DAS-DNBF, and the former NUA-DNBF emitted higher amount of N₂O. Analysis of abundance and composition profiles showed that denitrifying gene patterns varied more or less in two matrices with different depths at three sampling times. Burkholderiales, Rhodocyclales, and Rhizobiales were the most commonly detected in both media during stable periods. Denitrification was determined by the abundance of specific genes or their ratios as revealed by controlling factors. The enhanced nitrate removal could be due to increasing qnosZ or decreasing ∑qnir/qnosZ. Furthermore, NUA-DNBF solely reduced nitrate by increasing the denitrification enzyme activity.

Achieving partial denitrification through control of biofilm structure during biofilm growth in denitrifying biofilter

Partial denitrification was one of most effective ways to provide nitrite for annamox; whereas very limited research has been done to achieve nitrite accumulation in biofilm system. In this study, partial denitrification was studied in a lab-scale denitrifying biofilter (DNBF). The results showed biofilm structure variations caused the differences between nitrate specific reduction rate (NaSRR) and nitrite specific reduction rate (NiSRR), which led to nitrite accumulation in different degree at different biofilm formation phases. Hydrodynamic conditions also significantly influenced biofilm structure, nitrate and nitrite reduction activities. At the filtration velocity of 3.86mh^-1, not only biofilm structure, NaSRR and NiSRR kept relatively stable, but also 60% of nitrite accumulation and no nitrate in the effluent were achieved. Furthermore, Thauera genus bacteria, benefited for nitrite accumulation, became the dominant communities in high nitrite accumulation conditions. The partial denitrification combine with anammox in biofilter have the great potential applied in WWTPs.