A hybrid reed bed constructed wetland (HRBCW) with aeration system was employed in three-stages; a Surface-Flow (SF) system, a Vertical-Flow (VF) system, and lastly a Horizontal-Flow (HF) system in series. The system was planted with Malaysian native aquatic plant (Scirpus grossus) and it was made up of media arranged in three layers of medium gravel ( ϕ 10–15 mm) at the top, river sand ( ϕ 3–5 mm) in the middle, and larger gravel ( ϕ 30–35 mm) in the bottom of the CW. S. grossus could survive and reproduce with a continuous feed of 86.5 L raw wastewater per day. The results indicate that the system with a 3-day HRT achieved an average removal of 84.7 and 71.0% for NH4-N and PO4-P respectively. Based on this study, the use of HRBCW system for treating household sewage in small communities is a technically and economically feasible using S. grossus that has high effectiveness for treating domestic wastewater.

Performance of pilot Hybrid Reed Bed constructed wetland with aeration system on nutrient removal for domestic wastewater treatment

Nitrogen removal from wastewater with high ammonia nitrogen comcentration via shorter nitrification and denitrification

Microalgae have promising applications in wastewater treatment because of their ability to use inorganic compounds such as nitrates and phosphates as nutrients for their growth. Microalgae are applied to the secondary and tertiary bio-treatment with two benefits: i) pollutants removal from wastewater; ii) production of microalgal biomass, that can be exploited as a source of biomass and biomolecules. In the present work, four different microalgal strains (two from culture collections and two isolated from Sicilian littoral) were tested in municipal sewage bioremediation. The sewage of a municipal plant, already processed with primary treatment, was used for the cultivation of microalgal strains in order to test their potential on performing the secondary treatment. Microalgal cells were cultivated in growth medium and in sewage with the aim to compare their growth and biomass composition in different conditions. The efficiency of wastewater treatment was established through assessment of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorous (TP) of sewage before and after algal growth. Results showed that microalgal treatment alone is not effective in reducing COD and BOD, while all the tested strains were able to significantly reduce wastewater TN (up to 77 %) and TP (up to 61 %) concentrations. Amongst the tested strains, Chlorella genus can be considered the best candidate for wastewater treatment.

Autochthonous microalgae grown in municipal wastewaters as a tool for effectively removing nitrogen and phosphorous

Biological removal of selenate and ammonium by activated sludge in a sequencing batch reactor.

This study evaluated a novel shortcut biological nitrogen removal (BNR) method using activated sludge-biofilm coupled with microalgae in a photo-sequencing batch biofilm reactor (PSBBR) for treating high ammonia nitrogen (NH4+-N) wastewater. Results showed that the symbiotic microalgae supplied oxygen and an additional organic carbon source for bacteria. The consortium achieved high nitrogen removal efficiency (> 90%) and had the potential to lower the operating cost when used for treating biogas slurry (BS). It saved more than 50% of the external carbon source and reduced about 78% of oxygen demand compared with the conventional BNR process. Nitrogen was removed mainly through shortcut nitrification-denitrification (SCND) (> 80%) and biological assimilation (6.8%) in the PSBBR. The algal-bacterial symbiosis improved the species richness but reduced the microbial diversity of the biofilm. Nitrosomonas with an abundance of 19.81% was the dominant ammonia-oxidizing bacteria (AOB) in the biofilm, while Thauera with an abundance of 45.03% played a leading role in denitrification. This study concurrently indicated that algae and activated sludge coupling increased the nitrous oxide (N2O) emission in the shortcut nitrogen removal process.

Novel shortcut biological nitrogen removal using activated sludge-biofilm coupled with symbiotic algae

Two sequencing batch reactors, one with the conventional anoxic and aerobic (AO) process and the other with the multiple AO process, were operated to examine characteristics of biological nitrogen removal, especially of the multiple AO process. The long-term operation showed that the total nitrogen removal percentage of the multiple AO reactor was 38.7% higher than that of the AO reactor. In the multiple AO reactor, at the initial SBR cycle stage, due to the occurrence of simultaneous nitrification and denitrification, no nitrite and/or nitrate were accumulated. In the multiple AO reactor, activities of nitrite oxidizing bacteria were inhibited due to the multiple AO operating mode applied, resulting in the partial nitrification. Denitrifiers in the multiple AO reactor mainly utilized internal organic carbon for denitrification, and their activities were lower than those of denitrifiers in the AO reactor utilizing external organic carbon.

/pdf/characteristics-of-biological-nitrogen-removal-in-a-multiple-28ugs83zjn.pdf

Characteristics of Biological Nitrogen Removal in a Multiple Anoxic and Aerobic Biological Nutrient Removal Process

Nitrogen discharged from wastewater treatment plants contributes greatly to the eutrophication of receiving water bodies. The multiple anoxic and aerobic (AO) process can enhance nitrogen removal, while the concomitant emission of nitrous oxide (N2O) attracts growing attention. Nitrogen removal and N2O emission in a constant-flow multiple AO process were evaluated. The effects of dissolved oxygen (DO), carbon source, as well as feeding mode on N2O emission were investigated. The removal percentages of ammonia and total nitrogen were 99.8% and 74.1%, respectively. Limited DO, the presence of organic carbon, and high nitrite concentrations enhanced N2O emission during nitrification. Endogenous denitrification of nitrite showed a high N2O emission potential, especially for one-time dosing of nitrite. nosZ, encoding N2O reductase, was widely distributed in Proteobacteria (39.6%), β-proteobacteria (31.6%) and the genera of Ralstonia (20.0%). The study suggested that high DO concentration and the absence of organic carbon during nitrification, avoidance of endogenous denitrifying nitrite during denitrification, and the constant-feeding operation mode were all beneficial to minimize N2O emission.

Enhanced nitrogen removal and minimization of N2O emission in a constant-flow multiple anoxic and aerobic process

The present study aimed to optimize synthetic wastewater composition as a mixotrophic medium for enhanced growth and lipid accumulation coupled with high nitrogen removal by the green microalga Chlorella sp. Individual effects of the three main independent variables (nitrate concentration, seawater ratio, and glycerol supplementation) were tested initially, then response surface methodology (RSM) was subsequently performed to explore the optimum combined conditions. The highest lipid productivity of 37.60 mg/L day was recorded at 25% seawater. Glycerol supplementation enhanced both lipid content and biomass production, which resulted in the highest recorded lipid productivity of 42.61 mg/L day at 4 g/L glycerol. Central composite design followed by numerical optimization was further applied which suggested NaNO3 concentration at 101.5 mg/L, seawater ration of 23.8%, and glycerol supplementation of 0.25 g/L as the optimum conditions for dual maximum lipid productivity and nitrogen removal of 46.9 mg/L day and 98.0%, respectively. Under the optimized conditions, dry weight and lipid content increased by 31.9% and 20.3%, respectively, over the control, which resulted in increase in lipid productivity by 71.5%. In addition, optimization process resulted in pronounced changes in fatty acid proportions where saturated fatty acids increased by 7.4% in the optimized culture with simultaneous reduction of polyunsaturated fatty acids. The estimated biodiesel characteristics calculated from the fatty acid methyl ester (FAMEs) profile showed agreement with the international standards, while optimized cultures showed an 8.5% lower degree of unsaturation, which resulted in higher cetane numbers and lower iodine values. This study provides economical approach for optimization and efficient nutrient recycling through cultivation of Chlorella sp. for further enhanced biodiesel production.

/pdf/maximizing-nitrogen-removal-and-lipid-production-by-dsdugl2j.pdf

Maximizing Nitrogen Removal and Lipid Production by Microalgae under Mixotrophic Growth Using Response Surface Methodology: Towards Enhanced Biodiesel Production

Nitrogen removal and nitrous oxide (N2O) emission in a lab-scale constant-flow multiple anoxic (A) and aerobic (O) process, combined with the addition of suspended carriers, were investigated. Under steady state, 99.9% of ammonia nitrogen (NH4-N), 76.8% of orthophosphate, and 80.2% of total inorganic nitrogen removal efficiency was achieved. The N2O emission factor during nitrification was 0.8–1.9% of the oxidized NH4-N. The emission factor increased to 7.4–45.9% with the coexistence of heterotrophic activities. Extending the anoxic time from 30 to 90 min reduced the N2O emission factor from 1.6 to 1.0%. N2O emission was stimulated with nitrite (NO2-N) as the electron acceptor, with the N2O emission factor of 5.2–5.6%. Denitrification with internal organic carbon contributed 6.8% of reduced NO2-N to N2O. NO2-N might exert a crucial role in N2O emission independent of carbon source. For the acclimated microbial communities, Nitrospira and Nitrosospira were the dominant nitrifiers and responsible for the N2O emission during nitrification. Azospira, Dechloromonas, Flavobacterium, Pseudomonas, and unclassified genus of family Comamonadaceae might be responsible for N2O emission during denitrification. These findings may guide the design of multiple AO process for controlling N2O emission.

Nitrogen Removal and Nitrous Oxide Emission in a Constant-Flow Multiple Anoxic and Aerobic Process

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Papers

Characteristics of Biological Nitrogen Removal in a Multiple Anoxic and Aerobic Biological Nutrient Removal Process

Enhanced nitrogen removal and minimization of N2O emission in a constant-flow multiple anoxic and aerobic process

Maximizing Nitrogen Removal and Lipid Production by Microalgae under Mixotrophic Growth Using Response Surface Methodology: Towards Enhanced Biodiesel Production

Nitrogen Removal and Nitrous Oxide Emission in a Constant-Flow Multiple Anoxic and Aerobic Process