Evaluation of sustainable electron donors for nitrate removal in different water media

Reveling the micromolecular biological mechanism of acetate, thiosulfate and Fe0 in ecological floating beds for treating low C/N wastewater: Insight into nitrogen removals and greenhouse gases reductions

Selecting an appropriate electron donor to enhance nitrogen removal for treating low C/N wastewater in ecological floating beds (EFBs) is controversy. In this study, a systematic and comprehensive evaluation of sodium acetate (EFB-C), sodium thiosulfate (EFB-S) and iron scraps (EFB-Fe) was performed in a 2-year experiment on long-term viability including nitrogen removal and greenhouse gas emissions associated with key molecular biological mechanisms. The results showed that EFB-C (43-85 %) and EFB-S (40-88 %) exhibited superior total nitrogen (TN) removal. Temperature and hydraulic retention time (HRT) have significant impacts on TN removal of EFB-Fe, however, it could reach 86 % under high temperature (30-35 °C) and a long HRT (3 days), and it has lowest N2O (0-6.2 mg m-2 d-1) and CH4 (0-5.3 mg m-2 d-1) fluxes. Microbial network analysis revealed that the microbes changed from competing to cooperating after adding electron donors. A higher abundance of anammox genera was enriched in EFB-Fe. The Mantel's test and structural equation model provided proof of the differences, which showed that acetate and thiosulfate were similar, whereas Fe0 was different in the nitrogen removal mechanism. Molecular biology analyses further verified that heterotrophic, autotrophic, and mixotrophic coupled with anammox were the main TN removal pathways for EFB-C, EFB-S, and EFB-Fe, respectively. These findings provide a better understanding of the biological mechanisms for selecting appropriate electron donors for treating low C/N wastewater.

Effect of hydraulic retention time on denitrification performance and microbial communities of solid-phase denitrifying reactors using polycaprolactone/corncob composite

This study investigated the effect of hydraulic retention time (HRT) on the denitrification performance and microbial composition of reactors, packed with composite polycaprolactone and corncob carbon sources, during the treatment mariculture wastewater. The optimal HRT was 3 h, and average nitrogen removal efficiency was 99.00 %, 99.07 %, and 98.98 % in the HRT =3, 5, and 7 h groups, respectively. However, the 3 h group (DOC 2.91 mg/L) was the only group with a lower DOC concentration than that of the influent group (3.31 mg/L). Moreover, species richness was lower at HRT =3 h, with a greater proportion of denitrification-dominant phyla, such as Proteobacteria. The abundance of the NarG, NirK, and NirS functional genes suggested that the HRT =3 h group had a significant advantage in the nitrate and nitrite reduction phases. Under a short HRT, the composite carbon source achieved a good denitrification effect.

A collaborative effect of solid-phase denitrification and algae on secondary effluent purification

This study explored the collaborative effect on nutrients removal performance and microbial community in solid-phase denitrification based bacteria-algae symbiosis system. Three biodegradable carriers (apple wood, poplar wood and corncob) and two algae species (Chlorella vulgaris and Chlorella pyrenoidosa) were selected in these bacteria-algae symbiosis systems. Results demonstrated that corncob as the carrier exhibited the highest average removal efficiencies of total nitrogen (83.7%-85.1%) and phosphorus removal (38.1%-49.1%) in comparison with apple wood (65.8%-71.5%, 25.5%-32.7%) and poplar wood (42.5%-49.1%, 14.2%-20.7%), which was mainly attributed to the highest organics availability of corncob. The addition of Chlorella acquired approximately 3%-5% of promotion rates for nitrated removal among three biodegradable carriers, but only corncob reactor acquired significant promotions by 3%-11% for phosphorous removal. Metagenomics sequencing analysis further indicated that Proteobacteria was the largest phylum in all wood reactors (77.1%-93.3%) and corncob reactor without Chlorella (85.8%), while Chlorobi became the most dominant phylum instead of Proteobacteria (20.5%-41.3%) in the corncob with addition of Chlorella vulgaris (54.5%) and Chlorella pyrenoidosa (76.3%). Thus, the higher organics availability stimulated the growth of algae, and promoted the performance of bacteria-algae symbiosis system based biodegradable carriers.

Impacts of biostimulation and bioaugmentation on woodchip bioreactor microbiomes

IMPORTANCE

Nitrate pollution is a serious problem in agricultural areas in the U.S. Midwest and other parts of the world. Woodchip bioreactor is a promising technology that uses microbial denitrification to remove nitrate from agricultural subsurface drainage, although the reactor's nitrate removal performance is limited under cold conditions. This study showed that the inoculation of cold-adapted denitrifiers (i.e., bioaugmentation) and the addition of labile carbon (i.e., biostimulation) can influence the microbial populations and enhance the reactor's performance under cold conditions. This finding will help establish a strategy to mitigate nitrate pollution.

Systematic review: External carbon source for biological denitrification for wastewater

Nitrogen mitigation is serious environmental issue around the globe. Several methods for wastewater treatment have been introduced, but biological denitrification has been recommended, particularly with addition of the best external carbon source. The key sites of denitrification are wetlands; it can be carried out with different methods. To highlight the aforementioned technology, this paper deals to review the literature to evaluate biological denitrification and to demonstrate cost effective external carbon sources. The results of systematic review disclose the denitrification process and addition of different external carbon sources. The online literature exploration was accomplished using the most well-known databases, that is, science direct and the web of science database, resulting 625 review articles and 3084 research articles, published in peer-reviewed journals between 2015 and 2021 were identified in first process. After doing an in-depth literature survey and exclusion criteria, we started to shape the review from selected review and research articles. A number of studies confirmed that both nitrification and denitrification are significant for biological treatment of wastewater. The studies proved that the carbon source is the main contributor and is a booster for the denitrification. Based on the literature reviewed it is concluded that biological denitrification with addition of external carbon source is cost effective and best option in nitrogen mitigation in a changing world. Our study recommends textile waste for recovery of carbon source.

Denitrification performance and microbial community of bioreactor packed with PHBV/PLA/rice hulls composite

In this study, a novel biodegradable PHBV/PLA/rice hulls (PPRH) composite was applied and tested as biofilm attachment carrier and carbon source in two bioreactors for biological denitrification process. The denitrification performance, effect of operational conditions and microbial community structure of PPRH biofilm were evaluated. The batch experiment results showed that PPRH-packed bioreactor could completely remove 50 mg L^-1 of NO₃^--N at natural pH (ca. 7.5) and room temperature. The continuous flow experiments indicated that high NO₃^--N removal efficiency (77%-99%) was achieved with low nitrite (<0.48 mg L^-1) and ammonia (<0.81 mg L^-1) accumulation, when influent NO₃^--N concentration was 30 mg L^-1 and hydraulic retention time was 2-6 h. Furthermore, the microbial community analysis indicated that bacteria belonging to genus Diaphorobacter in phylum Proteobacteria were the most dominant and major denitrifiers in denitrification. In summary, PPRH composite was a promising carbon source for biological nitrate removal from water and wastewater.

Study on the properties of denitrifying carbon sources from cellulose plants and their nitrogen removal mechanisms

Carbon sources of cellulose plants are promising materials that enhance the activities of denitrifying bacteria in the groundwater system. To further verify the denitrification performance of cellulose plants and the main factors of affecting the denitrifying system, six cellulose plants from agricultural wastes (wood chip, corn cob, rice husk, corn straw, wheat straw, and sugar cane) were selected for bioavailable organic matter leaching experiments, carbon denitrification experiments, functional bacteria identification, and analysis experiments. The results show that the extracts of cellulose plants contain a mixed carbon sources system including small molecular organic acids, sugars, nitrogen-containing organic components, and esters. The qPCR results showed that the denitrifying bacteria had obvious advantages compared to anaerobic ammonia-oxidizing bacteria during the stable period; the denitrification experiment showed that each of six cellulose plants removed more than 80% of nitrogen, and the denitrification rates reached 1.00-2.00 mg N cm^-3·d^-1. The supplement of cellulose plants promotes the metabolism rate of denitrifying bacteria, and the additional denitrifying bacteria have little effect on nitrate removal. In summary, the expected denitrification reaction occurred in the cellulose plant system, which is suitable as a carbon source material for water body nitrogen pollution remediation.

Sustained Ability of a Natural Microbial Community to Remove Nitrate from Groundwater

Microbial-mediated nitrate removal from groundwater is widely recognized as the predominant mechanism for nitrate attenuation in contaminated aquifers and is largely dependent on the presence of a carbon-bearing electron donor. The repeated exposure of a natural microbial community to an electron donor can result in the sustained ability of the community to remove nitrate; this phenomenon has been clearly demonstrated at the laboratory scale. However, in situ demonstrations of this ability are lacking. For this study, ethanol (electron donor) was repeatedly injected into a groundwater well (treatment) for six consecutive weeks to establish the sustained ability of a microbial community to remove nitrate. A second well (control) located upgradient was not injected with ethanol during this time. The treatment well demonstrated strong evidence of sustained ability as evident by ethanol, nitrate, and subsequent sulfate removal up to 21, 64, and 68%, respectively, as compared to the conservative tracer (bromide) upon consecutive exposures. Both wells were then monitored for six additional weeks under natural (no injection) conditions. During the final week, ethanol was injected into both treatment and control wells. The treatment well demonstrated sustained ability as evident by ethanol and nitrate removal up to 20 and 21%, respectively, as compared to bromide, whereas the control did not show strong evidence of nitrate removal (5% removal). Surprisingly, the treatment well did not indicate a sustained and selective enrichment of a microbial community. These results suggested that the predominant mechanism(s) of sustained ability likely exist at the enzymatic- and/or genetic-levels. The results of this study demonstrated the in situ ability of a microbial community to remove nitrate can be sustained in the prolonged absence of an electron donor.

Exploration and verification of the feasibility of the sulfur-based autotrophic denitrification integrated biomass-based heterotrophic denitrification systems for wastewater treatment: From feasibility to application

The sulfur-based autotrophic denitrification (SAD) and the solid organic carbon-based denitrification processes are both efficient techniques to remove nitrate from wastewater, and the hydrogen ions generated by the SAD process would be consumed in the heterotrophic denitrification process. Therefore, it is possible to improve the denitrification capacity when the solid organic carbon was added into a SAD reactor. In this study, corncob powder and sawdust powder were selected as solid organic carbon sources, and the sulfur-based autotrophic denitrification integrated biomass-based heterotrophic denitrification system was formed (SBD). The laboratory and field experiments showed that SBD could shorten the start-up period, decrease the sulfate productivity, and maintain a good denitrification performance when treated wastewater. According to the field experiment results, when the HRT was 1 h, the effluent total nitrogen (TN) concentration was always lower than 15 mg L^-1. In addition, nitrite inhibition was observed when the concentration of nitrite in the reactors reached above 30 mg L^-1. The mixture of elemental sulfur powder, shell powder, corncob powder, and sawdust powder with a mass ratio of 6:2:1:1 was the optimal filter for the SBD system, with an average nitrate reduction rate (NAR) of 420 mg NO₃^-N·L^-1·d^-1 obtained at the end of the study. During the whole operation, the major autotrophs in the SBD systems were Thermomonas, Ferritrophicum, and Thiobacillus, while the major heterotrophs were Saprospiraceae, Ferruginibacter, Dokdonella, and Simplicispira. Overall, the SBD system was a feasible and practically favorable way to remove nitrate from wastewater.

Substrate type determines microbial activity and community composition in bioreactors for nitrate removal by denitrification at low temperature

High levels of nitrogen originating from blasting operations, for example at mining sites or quarries, risk contaminating water bodies through leaching from waste rock dumps. Woodchip bioreactors can be a simple and cost-effective way of reducing nitrate concentrations in the leachate. In this study we investigated how bottle sedge, barley straw, and pine woodchips used as electron donors for denitrification influenced microbial community composition and nitrate removal in lab-scale bioreactors during 270 days. The reactors were operated to ensure that nitrate was never limiting and to achieve similar nitrate removal (%). Distinct bacterial communities developed due to the different substrates, as determined by sequencing of the 16S rRNA gene. Sedge and straw reactors shared more taxa with each other than with woodchips and throughout the experimental period, sedge and straw were more diverse than woodchips. Cellulose degrading bacteria like Fibrobacteres and Verrucomicrobia were detected in the substrates after 100-150 days of operation. Nitrate removal rates were highest in the sedge and straw reactors. After initial fluctuations, these reactors removed 5.1-6.3 g N m^-3 water day^-1, which was 3.3-4.4 times more than in the woodchip reactors. This corresponded to 48%, 42%, and 44% nitrate removal for the sedge, straw, and woodchip reactors respectively. The functional communities were characterized by quantitative PCR and denitrification was the major nitrate removing process based on genetic potential and water chemistry, although sedge and straw developed a capacity for ammonification. Gene ratios suggested that denitrification was initially incomplete and terminating with nitrous oxide. An increase in abundances of nitrous oxide reducing capacity in all substrate types towards the end increased the potential for less emissions of the greenhouse gas nitrous oxide.

Metagenomic evidence reveals denitrifying community diversity rather than abundance drives nitrate removal in stormwater biofilters amended with different organic and inorganic electron donors

Various sole and mixed electron donors were tested to promote the denitrification rate and nitrate removal efficiency in biofilter systems with high phosphate and ammonia removal efficiency (92.6% and 95.3% respectively). Compared to sole electron donors, complex organic carbon (bits of wood and straw) substantially improved the denitrification rate and nitrate removal efficiency (from 6.3%-18.5% to35.4%) by shifting the denitrifying microbial community composition, even though the relative abundance of functional genes mediating denitrification decreased. The mixed electron donor combining complex organic carbon with sulfur, iron and CH₄ further promoted nitrate removal efficiency by 37.2%. The significantly higher abundance and diversity of bacteria mediating organic carbon decomposition in the treatments with complex organic carbon indicated the continuous production of organic carbon with small molecular weights, which provided sustainable and effective electron donor for denitrification. However, sole sulfur or iron did not effectively promote the denitrification rate and nitrogen removal efficiency, even though the related microbial community had been formed.

Bio-denitrification performance enhanced by graphene-facilitated iron acquisition

Bio-denitrification is widely used for remediation of nitrate contaminated site or removal of nitrate from wastewater, but its efficiency is not always satisfied and high nitrite accumulation and nitrous oxide emission occur frequently. Iron plays an important role in achieving efficient biological denitrification. Nevertheless, its concentration in cells is usually inadequate, and additional supply of iron to denitrification system has been adopted in the literature. In this study, a novel approach to increase the intracellular iron concentration of denitrifying microbes by using graphene to accelerate iron transport, which significantly enhanced bio-denitrification and decreased intermediates accumulations, was reported, and the underlying mechanisms were explored. The presence of 50 mg/L of graphene was observed to not only significantly promote nitrate removal efficiency by 67.3%, but also decrease nitrite and nitrous oxide generation by 49.0% and 63.9%, respectively. It was found that graphene promoted the generation, transfer and consumption of electrons, increased the activities or gene expressions of Fe-containing enzymes (such as complex I, complex III, various cytochromes, and most denitrification reductases), and enhanced the growth of denitrifiers due to iron acquisition by denitrifying bacteria being remarkably facilitated, leading to a significant increment of intracellular iron concentration. Meanwhile, the intracellular proton-motive force and ATP levels were promoted as well. This study provided a new approach to enhancing bio-denitrification and revealed a novel insight into biological iron acquisition.

Nitrogen removal performance in pilot-scale solid-phase denitrification systems using novel biodegradable blends for treatment of waste water treatment plants effluent

In this study, three pilot-scale solid-phase denitrification (SPD) systems filled with poly-3-hydroxybutyrate-co-hyroxyvelate (PHBV), PHBV-Rice hulls (PHBV-RH) and PHBV-Sawdust (PHBV-S) were operated to treat effluent of waste water treatment pangts (WWTPs). The fast start-up and intensified nitrogen removal performance were obtained in PHBV-RH and PHBV-S systems. Besides, the optimal total nitrogen (TN) removal efficiency was obtained in PHBV-S system (91.65 ± 4.12%) with less ammonia accumulation and dissolved organic carbon (DOC) release. The significant enrichment of amx 16S rRNA and nirS genes in PHBV-RH and PHBV-S systems indicated the possible coexistence of anammox and denitrification. Miseq sequencing analysis exhibited more complex community diversity, more abundant denitrifying and fermenting bacteria in PHBV-RH and PHBV-S systems. The co-existence of denitrification and anammox might contribute to better control of nitrogen and dissolved organic carbon in PHBV-S system. The outcomes provide an economical and eco-friendly alternative to improve nitrogen removal of WWTPs effluent.

The impact of media, plants and their interactions on bioretention performance: A review

Bioretention systems have gained considerable popularity as a more natural approach to stormwater management in urban environments. The choice of bioretention media is frequently cited as one of the critical design parameters with the ultimate impact on the performance of the system. The goal of this review is to highlight data that challenge the importance of media as being the dominant design parameter and argue that the long-term performance is shaped by the interactions between media and the living components of a bioretention system, especially vegetation. Some of the key interactions are related to the impact of plant roots on media pore structure, which has implications on infiltration, storage capacity, and treatment. Another relevant interaction pertains to evapotranspiration and the associated impacts on the water balance and the water quality performance of bioretention systems. The impacts of vegetation on the media are highlighted and actual, as well as potential, impacts of plant-media interactions on bioretention performance are presented.

Seasonal operation of dual-mode biofilters: The influence of plant species on stormwater and greywater treatment

The use of stormwater biofilters (also known as bioretention systems and raingardens), in tropical and semi-arid areas is hindered by seasonal rainfall patterns which cause extended dry periods. These periods can result in plant die-off, long-term damage to system health and leaching of pollutants when stormwater inflows resume. Using an additional polluted water source during dry periods could minimise system stress and eliminate the need to irrigate biofilters with potable water during dry spells. As such, the presented laboratory study tested the seasonal operation of biofilters, by switching from stormwater treatment in wet months to greywater treatment in dry months. Forty-five single planted biofilter columns, incorporating sedges, grasses, understory ornamentals and vines, were subjected to four months of stormwater inflows, followed by three months of greywater inflows. We also investigated the impact of including a carbon source in the saturated zone on treatment performance. The results showed plant species selection to be critical for nitrogen and phosphorus removal, with consistently effective species such as Carex appressa and Canna x generalis able to maintain low outflow concentrations (e.g. total nitrogen of 0.2-0.3 mg/L and 0.3-0.6 mg/L, respectively) across both water sources. Low outflow phosphorus concentrations were associated with plant species that had high filterable reactive phosphorus removal across both water sources. Similarly, higher removal of ammonia and oxidised nitrogen was associated with lower overall nitrogen concentrations. In contrast, high removal of total suspended sediment (>94%), biochemical oxygen demand (>98%) and some heavy metals (e.g. lead >98% and copper >93%) was reported across all designs. The results suggest that with the careful selection of plant species, biofilters can be operated seasonally as a feasible and practical solution to maintaining system health during extended dry periods.

A Review of Nitrogen Removal for Urban Stormwater Runoff in Bioretention System

One of the best management practices (BMPs) for stormwater quality and quantity control is a bioretention system. The removal efficiency of different pollutants under this system is generally satisfactory, except for nitrogen which is deficient in certain bioretention systems. Nitrogen has a complex biogeochemical cycle, and thus the removal processes of nitrogen are typically slower than other pollutants. This study summarizes recent studies that have focused on nitrogen removal for urban stormwater runoff and discusses the latest advances in bioretention systems. The performance, influencing factors, and design enhancements are comprehensively reviewed in this paper. The review of current literature reveals that a bioretention system shows great promise due to its ability to remove nitrogen from stormwater runoff. Combining nitrification and denitrification zones with the addition of a carbon source and selecting different plant species promote nitrogen removal. Nevertheless, more studies on nitrogen transformations in a bioretention system and the relationships between different design factors need to be undertaken.

Dual-mode stormwater-greywater biofilters: The impact of alternating water sources on treatment performance

The intermittent nature of stormwater runoff impacts the treatment performance of biofilters, also known as stormwater biofiltration or bioretention systems and raingardens. During extended dry periods, which are common even in temperate climates, plants can perish, creating unattractive and non-functional systems that might leach pollutants during the next rainfall event. The current solution is to irrigate during long dry spells, which is costly and unsustainable as biofilters become more widespread. This paper presents the development of dual-mode biofilters, where stormwater and greywater are treated within the same system. Fifty columns, utilising eight plant species, including understory and climbing ornamentals, and designs with and without a carbon source in the submerged zone, were subjected to alternating greywater and stormwater inflows over five months. Six sampling events investigated treatment performance across these switching inflows and an extended dry period (atypical event). Good removal of total suspended solids (>83%), biochemical oxygen demand (>86%) and some heavy metals (e.g. lead >96%) were reported irrespective of design. Plant species selection was critical for the removal of nitrogen (2 to 79%) and phosphorus (12 to 75%) under dual-mode operation. However, following the extended dry period, plants with the lowest nutrient outflow concentrations also experienced some of the highest sediment and carbon concentrations, suggesting that a mixture of plant species may be beneficial for withstanding abnormal conditions. Differences between the treatment performance of designs with and without a carbon source were negligible, with potential benefits possibly negated due to the increased root mass that comes with age (systems were approximately two years old) and the release of carbon from root exudates. The results demonstrate the potential for dual-mode stormwater-greywater biofilters as an alternative to single-mode systems as they can provide effective treatment, along with greater volumes of treated water, while maintaining system performance throughout the year.

The metabolic activity of denitrifying microorganisms accumulating polyphosphate in response to addition of fusel oil

The effect of distillery waste product (fusel oil) as an alternative external organic carbon source (EOCS) was investigated in terms of the metabolic properties of denitrifying polyphosphate accumulating organisms (DPAOs). Samples of the non-acclimated biomass were collected from a local full-scale wastewater treatment plant employing A²/O type bioreactors. The acclimated biomass was obtained after cultivation (with fusel oil added) in a bench-scale reactor with a process configuration similar to the full-scale bioreactor. Changes in the functional properties of the biomass were investigated by measuring the phosphate release/uptake rates (PRRs and PURs), and nitrate utilization rates (NURs) with fusel oil in anaerobic-anoxic batch tests. Furthermore, a validated extended Activated Sludge Model no 2d (ASM2d) was used as a supporting tool to analyze the experimental results and estimate the contribution of DPAOs to the overall denitrification. In the non-acclimated biomass with fusel oil, the PRRs, PURs and NURs were low and close to the rates obtained in a reference test without adding EOCS. With the acclimated biomass, the PUR and NUR increased significantly, i.e., 3.5 and 2.7 times, respectively. In the non-acclimated biomass, approximately 60.0 ± 3.6% and 20.0 ± 2.2% of the total NUR was attributed to the utilization of endogenous carbon and examined EOCS, respectively. The remaining portion (20% of the total NUR) was attributed to PHA utilization (linked to PO₄-P uptake) by DPAOs. With the acclimated biomass, the contribution of the EOCS to the NUR increased to approximately 60%, while the contribution of the endogenous carbon source decreased accordingly. Very accurate predictions of PURs and NURs (R² = 0.97–1.00) were obtained with the extended ASM2d. Based on model simulations, it was estimated that the activity of DPAOs and denitrifying ordinary heterotrophic organisms corresponded to approximately 20% and 80% of the total NUR, respectively.

Biological denitrification in marine aquaculture systems: A multiple electron donor microcosm study

There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toilet flushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S⁰) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m³·d)), followed by FW (4.5 g N/(m³·d)), S⁰ (3.5 g N/(m³·d)), eucalyptus mulch (2.6 g N/(m³·d)), and eucalyptus mulch with sulfur (2.2 g N/(m³·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak ≫ eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2-11.9 g N/(m³·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.

The production of cyanobacterial carbon under nitrogen-limited cultivation and its potential for nitrate removal

Harmful cyanobacterial blooms (CyanoHABs) represent a serious threat to aquatic ecosystems. A beneficial use for these harmful microorganisms would be a promising resolution of this urgent issue. This study applied a simple method, nitrogen limitation, to cultivate cyanobacteria aimed at producing cyanobacterial carbon for denitrification. Under nitrogen-limited conditions, the common cyanobacterium, Microcystis, efficiently used nitrate, and had a higher intracellular C/N ratio. More importantly, organic carbons easily leached from its dry powder; these leachates were biodegradable and contained a larger amount of dissolved organic carbon (DOC) and carbohydrates, but a smaller amount of dissolved total nitrogen (DTN) and proteins. When applied to an anoxic system with a sediment-water interface, a significant increase of the specific NO_X^--N removal rate was observed that was 14.2 times greater than that of the control. This study first suggests that nitrogen-limited cultivation is an efficient way to induce organic and carbohydrate accumulation in cyanobacteria, as well as a high C/N ratio, and that these cyanobacteria can act as a promising carbon source for denitrification. The results indicate that application as a carbon source is not only a new way to utilize cyanobacteria, but it also contributes to nitrogen removal in aquatic ecosystems, further limiting the proliferation of CyanoHABs.

Application of denitrifying wood chip bioreactors for management of residential non-point sources of nitrogen

Two important and large non-point sources of nitrogen in residential areas that adversely affect water quality are stormwater runoff and effluent from on-site treatment systems. These sources are challenging to control due to their variable flow rates and nitrogen concentrations. Denitrifying bioreactors that employ a lignocellulosic wood chip medium contained within a saturated (anoxic) zone are relatively new technology that can be implemented at the local level to manage residential non-point nitrogen sources. In these systems, wood chips serve as a microbial biofilm support and provide a constant source of organic substrate required for denitrification. Denitrifying wood chip bioreactors for stormwater management include biofilters and bioretention systems modified to include an internal water storage zone; for on-site wastewater, they include upflow packed bed reactors, permeable reactive barriers, and submerged wetlands. Laboratory studies have shown that these bioreactors can achieve nitrate removal efficiencies as high as 80-100% but could provide more fundamental insight into system design and performance. For example, the type and size of the wood chips, hydraulic loading rate, and dormant period between water applications affects the hydrolysis rate of the lignocellulosic substrate, which in turn affects the amount and bioavailability of dissolved organic carbon for denitrification. Additional field studies can provide a better understanding of the effect of varying environmental conditions such as ambient temperature, precipitation rates, household water use rates, and idle periods on nitrogen removal performance. Long-term studies are also essential for understanding operations and maintenance requirements and validating mathematical models that integrate the complex physical, chemical, and biological processes occurring in these systems. Better modeling tools could assist in optimizing denitrifying wood chip bioreactors to meet nutrient reduction goals in urban and suburban watersheds.

Designing living walls for greywater treatment

Greywater is being increasingly used as an alternative water source to reduce potable water demand and to alleviate pressure on sewerage systems. This paper presents the development of a low energy and low maintenance greywater treatment technology: a living wall system, employing ornamental plants (including vines) grown in a sand filter on a side of a building to treat shower, bath, and washing basin wastewaters. The system can, at the same time, provide critical amenity and micro-climate benefits to our cities. A large scale column study was conducted in Melbourne, Australia, to investigate the following design and operational factors of the proposed system: plant species, saturated zone design, rest period, hydraulic loading rate and pollutant inflow concentration. The results indicate that the use of ornamental species (e.g. Canna lilies, Lonicera japonica, ornamental grape vine) can contribute to pollutant removal. Vegetation selection was found to be particularly important for nutrient removal. While a wider range of tested plant species was effective for nitrogen removal (>80%), phosphorus removal was more variable (-13% to 99%) over the study period, with only a few tested plants being effective - Carex appressa and Canna lilies were the best performers. It was also found that phosphorus removal can be compromised over the longer term as a result of leaching. Excellent suspended solids and organics removal efficiencies can be generally achieved in these systems (>80% for TSS and >90% for BOD) with plants having a relatively small impact. Columns had an acceptable infiltration capacity after one year of operation. When planted with effective species (e.g. Carex appressa and Canna lilies), it is expected that performance will not be significantly affected by longer rest periods and higher pollutant concentrations in the early years of system operation. The results of this study, thus, demonstrate that innovative and aesthetically pleasing living walls can be designed for treatment of greywater at the household scale.

Denitrifying bioreactor clogging potential during wastewater treatment

Chemoheterotrophic denitrification technologies using woodchips as a solid carbon source (i.e., woodchip bioreactors) have been widely trialed for treatment of diffuse-source agricultural nitrogen pollution. There is growing interest in the use of this simple, relatively low-cost biological wastewater treatment option in waters with relatively higher total suspended solids (TSS) and chemical oxygen demand (COD) such as aquaculture wastewater. This work: (1) evaluated hydraulic retention time (HRT) impacts on COD/TSS removal, and (2) assessed the potential for woodchip clogging under this wastewater chemistry. Four pilot-scale woodchip denitrification bioreactors operated for 267 d showed excellent TSS removal (>90%) which occurred primarily near the inlet, and that COD removal was maximized at lower HRTs (e.g., 56% removal efficiency and 25 g of COD removed per m³ of bioreactor per d at a 24 h HRT). However, influent wastewater took progressively longer to move into the woodchips likely due to a combination of (1) woodchip settling, (2) clogging due to removed wastewater solids and/or accumulated bacterial growth, and (3) the pulsed flow system pushing the chips away from the inlet. The bioreactor that received the highest loading rate experienced the most altered hydraulics. Statistically significant increases in woodchip P content over time in woodchip bags placed near the bioreactor outlets (0.03 vs 0.10%P₂O₅) and along the bioreactor floor (0.04 vs. 0.12%P₂O₅) confirmed wastewater solids were being removed and may pose a concern for subsequent nutrient mineralization and release. Nevertheless, the excellent nitrate-nitrogen and TSS removal along with notable COD removal indicated woodchip bioreactors are a viable water treatment technology for these types of wastewaters given they are used downstream of a filtration device.

Effective biodegradation of nitrate, Cr(VI) and p-fluoronitrobenzene by a novel three dimensional bioelectrochemical system

p-Fluoronitrobenzene (p-FNB) was degraded in a novel three dimensional bioelectrochemical system (3D BES) and potentially utilized as carbon source for achieving both nitrate (NO3(-)−N) and Cr(VI) reduction. For single NO3(-)−N and Cr(VI) removal, 200 mg L(-1) NO3(-)−N and 100 mg L(-1) Cr(VI) could be almost completely converted to N2 and Cr(III) at current 50 mA. For single p-FNB degradation, 100 mg L(-1) p-FNB was completely degraded at current 50 mA. The critical current for defluorination was 40 mA, and the intermediate product p-fluoroaniline (p-FA) tended to decrease when current was higher than 40 mA. When NO3(-)−N, Cr(VI), and p-FNB were both coexisted in this system, the average NO3(-)−N, Cr(VI), and p-FNB removal efficiencies slightly decreased with addition of carbon source. Without carbon source, NO3(-)−N and Cr(VI) removal rates reached 34.45% and 41.38% with 91.02% p-FNB degradation, proving that NO3(-)−N and Cr(VI) could be reduced by degrading p-FNB in the BES.