Nitrifying bio-cord reactor: performance optimization and effects of substratum and air scouring

Design strategy and mechanism of nitrite oxidation suppression of elevated loading rate partial nitritation system

There is a current need for a low operational intensity, effective and small footprint system to achieve stable partial nitritation for subsequent anammox treatment at mainstream municipal wastewaters. This research identifies a unique design strategy using an elevated total ammonia nitrogen (TAN) surface area loading rate (SALR) of 5 g TAN/m2.d to achieve cost-effective, stable, and elevated rates of partial nitritation in a moving bed biofilm reactor (MBBR) system under mainstream conditions. The elevated loaded partial nitritation MBBR system achieves a TAN surface area removal rate (SARR) of 2.01 ± 0.07 g TAN/m2.d and NO2−-N: NH4+-N stoichiometric ratio of 1.15:1, which is appropriate for downstream anammox treatment. The elevated TAN SALR design strategy promotes nitrite-oxidizing bacteria (NOB) activity suppression rather than a reduction in NOB population as the reason for the suppression of nitrite oxidation in the mainstream elevated loaded partial nitritation MBBR system. NOB activity is limited at an elevated TAN SALR likely due to thick biofilm embedding the NOB population and competition for dissolved oxygen (DO) with ammonia-oxidizing bacteria for TAN oxidation to nitrite within the biofilm structure, which ultimately limits the uptake of DO by NOB in the system. Therefore, this design strategy offers a cost-effective and efficient alternative for mainstream partial nitritation MBBR systems at water resource recovery facilities.

Use of life cycle assessment and water quality analysis to evaluate the environmental impacts of the bioremediation of polluted water

The lakes along the Yangtze River are important source of pollutants that ultimately flow from the river into the East China Sea. Bioremediation is a green technology used to treat polluted water in lakes along the Yangtze River. Life cycle assessment and a comprehensive water quality index are used to evaluate the potential environmental impacts of constructed wetlands (CWs), ecological floating beds (EFBs), and combined ecological floating beds (CEFBs). The results showed that the raw material acquisition, construction, and operation of the CWs, EFBs, and CEFBs accounted for 24.1%, 35.3%, and 40.6%, respectively, of the total environmental impact. The acquisition of raw materials to construct the bioremediation system accounted for 51.6% of the total environmental impact. Among the nine impact categories considered, the system's global warming potential was the largest. Among the three stages of the project (raw material acquisition, construction, and operation), construction had the largest impact on eutrophication (the eutrophic potential of the construction stage was the largest). Furthermore, the operation of the project reduced the human eco-toxicity potential. The evaluation of the water quality before and after implementing the project revealed that CEFBs purified the water more effectively than CWs and EFBs did, particularly with respect to the removal of the total phosphorus.

Autotrophic Fixed-Film Systems Treating High Strength Ammonia Wastewater

The aim of the study was enrichment of nitrifying bacteria and to investigate the potential of autotrophic fixed-film and hybrid bioreactors to treat high strength ammonia wastewater (up to 1,000 mg N/L). Two types of fixed-film systems [moving bed biofilm reactor (MBBR) and BioCord^TM] in two different configurations [sequencing batch reactor (SBR) and a continuous stirred tank reactor (CSTR)] were operated for 306 days. The laboratory-scale bioreactors were seeded with activated sludge from a municipal wastewater treatment plant and fed synthetic wastewater with no organics. Strategies for acclimation included biomass reseeding (during bioreactor start-up), and gradual increase in the influent ammonia concentration [from 130 to 1,000 mg N/L (10% every 5 days)]. Stable ammonia removal was observed up to 750 mg N/L from 45 to 145 days in the MBBR SBR (94-100%) and CSTR (72-100%), and BioCord^TM SBR (96-100%) and CSTR (92-100%). Ammonia removal declined to 87% ± 6, in all bioreactors treating 1,000 mg N/L (on day 185). Following long-term operation at 1,000 mg N/L (on day 306), ammonia removal was 93-94% in both the MBBR SBR and BioCord^TM CSTR; whereas, ammonia removal was relatively lower in MBBR CSTR (20-35%) and BioCord^TM SBR (45-54%). Acclimation to increasing concentrations of ammonia led to the enrichment of nitrifying (Nitrosomonas, Nitrospira, and Nitrobacter) and denitrifying (Comamonas, OLB8, and Rhodanobacter) bacteria [16S rRNA gene sequencing (Illumina)] in all bioreactors. In the hybrid bioreactor, the nitrifying and denitrifying bacteria were relatively more abundant in flocs and biofilms, respectively. The presence of dead cells (in biofilms) suggests that in the absence of an organic substrate, endogenous decay is a likely contributor of nutrients for denitrifying bacteria. The nitrite accumulation and abundance of denitrifying bacteria indicate partial denitrification in fixed-film bioreactors operated under limited carbon conditions. Further studies are required to assess the contribution of organic material produced in autotrophic biofilms (by endogenous decay and soluble microbial products) to the overall treatment process. Furthermore, the possibility of sustaining autotrophic nitrogen in high strength waste-streams in the presence of organic substrates warrants further investigation.

Optimization of nutrient removal of novel electrochemically active carriers by response surface methodology

In order to improve the nutrient removal capacity of the carriers in the integrated fixed-film activated sludge (IFAS) system, a novel electrochemically active carrier was developed in this study. The nutrient removal performance of the carrier under different operating conditions was deeply investigated based on response surface methodology. The higher concentration of mixed liquor suspended solid (MLSS) and lower dissolved oxygen (DO) value inhibited ammonium (NH₄⁺-N) removal performance of the carrier, while promoted total nitrogen (TN) depletion. Lower influent C/N ratio favored denitrification of the carrier. In addition, it was found that the enhanced removal of NH₄⁺-N and TN in IFAS depended not only on the increase of carrier biomass, but also on the electrochemical activity of the novel carrier. Under the most effective conditions, the novel carrier could improve the TN removal efficiency by 19.7% compared with the activated sludge process.

Partial nitritation at elevated loading rates: design curves and biofilm characteristics

There is a need to develop low operational intensity, cost-effective, and small-footprint systems to treat wastewater. Partial nitritation has been studied using a variety of control strategies, however, a gap in passive operation is evident. This research investigates the use of elevated loading rates as a strategy for achieving low operational intensity partial nitritation in a moving bed biofilm reactor (MBBR) system. The effects of loading rates on nitrification kinetics and biofilm characteristics were determined at elevated, steady dissolved oxygen concentrations between 5.5 and 7.0 mg O₂/L and ambient temperatures between 19 and 21 °C. Four elevated loading rates (3, 4, 5 and 6.5 g NH₄⁺-N/m² days) were tested with a distinct shift in kinetics being observed towards nitritation at elevated loadings. Complete partial nitritation (100% nitrite production) was achieved at 6.5 g NH₄⁺-N/m² days, likely due to thick biofilm (572 µm) and elevated NH₄⁺-N load, which resulted in suppression of nitrite oxidation.