Control of non-point source pollution by a natural wetland

Abundance, community and driving factor of nitrifiers in western China plateau

Complete ammonia oxidation (comammox) is one of the most important biogeochemical processes, with recent studies showing that comammox process dominates nitrification in many ecosystems. However, the abundance, community and driving factor of comammox bacteria and other nitrifying microorganisms in plateau wetland is still unclear. Here, the abundances and community features of comammox bacteria, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the wetland sediments of western China plateaus were examined using qPCR and high-throughput sequencing. The results indicate that comammox bacteria were more abundant than AOA and AOB, and dominated the nitrification process. Compared with low-elevation samples (below 3000 m: samples 6-10, 12, 13, 15, 16), the abundance of comammox bacteria was much higher at high-elevation samples (above 3000 m: samples 1-5, 11, 14, 17, 18). The key species of AOA, AOB, and comammox bacteria were Nitrososphaera viennensis, Nitrosomonas europaea, and Nitrospira nitrificans, respectively. The key factor affecting comammox bacteria community was elevation. Elevation could increase the interaction links of key species Nitrospira nitrificans, resulting in high comammox bacterial abundance. The results of this study advance our knowledge of comammox bacteria in natural ecosystems.

Mitigating the global expansion of harmful cyanobacterial blooms: Moving targets in a human- and climatically-altered world

Cyanobacterial harmful algal blooms (CyanoHABs) are a major threat to human and environmental health. As global proliferation of CyanoHABs continues to increase in prevalence, intensity, and toxicity, it is important to identify and integrate the underlying causes and controls of blooms in order to develop effective short- and long-term mitigation strategies. Clearly, nutrient input reductions should receive high priority. Legacy effects of multi-decadal anthropogenic eutrophication have altered limnetic systems such that there has been a shift from exclusive phosphorus (P) limitation to nitrogen (N) limitation and N and P co-limitation. Additionally, climate change is driving CyanoHAB proliferation through increasing global temperatures and altered precipitation patterns, including more extreme rainfall events and protracted droughts. These scenarios have led to the "perfect storm scenario"; increases in pulsed nutrient loading events, followed by persistent low-flow, long water residence times, favoring bloom formation and proliferation. To meet the CyanoHAB mitigation challenge, we must: (1) Formulate watershed and airshed-specific N and P input reductions on a sliding scale to meet anthropogenic and climatic forcings. (2) Develop CyanoHAB management strategies that incorporate current and anticipated climatic changes and extremes. (3) Make nutrient management strategies compatible with other physical-chemical-biological mitigation approaches, such as altering freshwater flow and flushing, dredging, chemical applications, introduction of selective grazers, etc. (4) Target CyanoHAB toxin production and developing management approaches to reduce toxin production. (5) Develop broadly applicable long-term strategies that incorporate the above recommendations.

Optical properties of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) levels in constructed water treatment wetland systems in southern California, USA

Many removal mechanisms in treatment wetlands involve absorption to organic matter. Optical properties and DOC levels of waters entering and exiting 4 treatment wetland systems in Orange County, Southern California, were measured to characterize the dissolved organic matter pool. Average DOC levels decreased between the inlets and outlets, except for Forge Street (FS), which increased. For 3 wetlands, absorption coefficients decreased between inlet and outlet; the exception was FS, which increased. Average spectral slopes for the inlets and outlets were similar. Average intensities of terrestrial humic peaks A and C from 3D EEM fluorescence spectra decreased between the inlets and outlets for most wetlands. No EEM protein peaks were observed. Average flu/abs ratios for inlets and outlets were similar (high point for FS inlet excluded), suggesting chromophoric dissolved organic matter (CDOM) of a similar composition was present. The average FI value for the inlets and outlets was ∼1.5, consistent with terrestrial sources of CDOM. Average BIX values for the inlets and outlets were ∼0.8, suggesting limited contributions from autochthonous production of CDOM. Dominant plant species in the wetlands were cattail and bulrush. Humic peaks A and C, along with protein peaks, were observed in plant leachates. Protein peaks rapidly degraded with solar simulator irradiation. Results indicate that most of the wetlands are a net sink for CDOM, possibly due to absorption to sediments. The FS wetland appears to have a source of non-CDOM optically active organic carbon, possibly from a pollutant.

Combined industrial wastewater treatment in anaerobic bioreactor posttreated in constructed wetland

Constructed wetland (CW) with monoculture of Arundo donax L. was investigated for the posttreatment of anaerobic bioreactor (ABR) treating combined industrial wastewater. Different dilutions of combined industrial wastewater (20, 40, 60, and 80) and original wastewater were fed into the ABR and then posttreated by the laboratory scale CW. The respective removal efficiencies of COD, BOD, TSS, nitrates, and ammonia were 80%, 78-82%, 91.7%, 88-92%, and 100% for original industrial wastewater treated in ABR. ABR was efficient in the removal of Ni, Pb, and Cd with removal efficiencies in the order of Cd (2.7%) > Ni (79%) > Pb (85%). Posttreatment of the ABR treated effluent was carried out in lab scale CW containing A. donax L. CW was effective in the removal of COD and various heavy metals present in ABR effluents. The posttreatment in CW resulted in reducing the metal concentrations to 1.95 mg/L, 0 mg/L, and 0.004 mg/L for Ni, Pb, and Cd which were within the permissible water quality standards for industrial effluents. The treatment strategy was effective and sustainable for the treatment of combined industrial wastewater.

Natural treatment systems as sustainable ecotechnologies for the developing countries

The purpose of natural treatment systems is the re-establishment of disturbed ecosystems and their sustainability for benefits to human and nature. The working of natural treatment systems on ecological principles and their sustainability in terms of low cost, low energy consumption, and low mechanical technology is highly desirable. The current review presents pros and cons of the natural treatment systems, their performance, and recent developments to use them in the treatment of various types of wastewaters. Fast population growth and economic pressure in some developing countries compel the implementation of principles of natural treatment to protect natural environment. The employment of these principles for waste treatment not only helps in environmental cleanup but also conserves biological communities. The systems particularly suit developing countries of the world. We reviewed information on constructed wetlands, vermicomposting, role of mangroves, land treatment systems, soil-aquifer treatment, and finally aquatic systems for waste treatment. Economic cost and energy requirements to operate various kinds of natural treatment systems were also reviewed.

Organic matter and nitrogen removal within field-scale constructed wetlands: reduction performance and microbial identification studies

This study investigated organic matter and nitrogen reduction and transformation mechanisms within a field-scale hybrid natural purification system. The system included an oxidation pond, two serial surface-flow wetlands with a cascade in between, and a subsurface-flow wetland receiving secondary treated dormitory sewage. The average biochemical oxygen demand (BOD) and chemical oxygen demand (COD) removal was 81 and 48%, respectively. Microbial degradation was the primary process contributing to organic reduction. Total Kjeldahl nitrogen (TKN) and ammonium decreased from 7.1 to 3.9 and 5.58 to 3.25 mg/L, respectively, within the surface-flow wetlands. The results indicated that nitrification occurred within the aerobic compartments. The nitrate levels continued to decrease from 1.26 to 1.07 mg/L, indicating nitrate reduction occurred in the surface-flow wetland. Total nitrogen decreased from 8.61 to 5.12 mg/L, equivalent to a 41% reduction, within the surface-flow wetlands. Results revealed that denitrification might concurrently occur in the compartment of surface-flow wetland. Total nitrogen continued to decrease from 5.12 to 3.99 mg/L within the anoxic subsurface-flow wetlands through denitrification transformation. The significant total nitrogen reduction observed was 65%. The predominant reduction of total nitrogen might take place within the sediment of surface flow and the subsurface-flow wetland where denitrification occurred. The microbial identification results also indicated that nitrification/denitrification might occur concurrently within the sediments of surface-flow wetlands. The results of this study show that hybrid wetland systems are a viable option for organic matter and nitrogen transformation and removal in tropical regions where tertiary wastewater systems are too costly or unable to operate. Treated water from these systems can comply with local surface water criteria rendering water for reuse and groundwater recharge.

Application of a constructed wetland for industrial wastewater treatment: a pilot-scale study

The main objective of this study was to examine the efficacy and capacity of using constructed wetlands on industrial pollutant removal. Four parallel pilot-scale modified free water surface (FWS) constructed wetland systems [dimension for each system: 4-m (L)x1-m (W)x1-m (D)] were installed inside an industrial park for conducting the proposed treatability study. The averaged influent contains approximately 170 mg l(-1) chemical oxygen demand (COD), 80 mg l(-1) biochemical oxygen demand (BOD), 90 mg l(-1) suspend solid (SS), and 32 mg l(-1) NH(3)-N. In the plant-selection study, four different wetland plant species including floating plants [Pistia stratiotes L. (P. stratiotes) and Ipomoea aquatica (I. aquatica)] and emergent plants [Phragmites communis L. (P. communis) and Typha orientalis Presl. (T. orientalis)] were evaluated. Results show that only the emergent plant (P. communis) could survive and reproduce with a continuous feed of 0.4m(3)d(-1) of the raw wastewater. Thus, P. communis was used in the subsequent treatment study. Two different control parameters including hydraulic retention time (HRT) (3, 5, and 7d) and media [vesicles ceramic bioballs and small gravels, 1cm in diameter] were examined in the treatment study. Results indicate that the system with a 5-d HRT (feed rate of 0.4m(3)d(-1)) and vesicles ceramic bioballs as the media had the acceptable and optimal pollutant removal efficiency. If operated under conditions of the above parameters, the pilot-plant wetland system can achieve removal of 61% COD, 89% BOD, 81% SS, 35% TP, and 56% NH(3)-N. The treated wastewater meets the current industrial wastewater discharge standards in Taiwan.