Eutrophication Of Surface Waters Research Articles

A review on bioflocculation using microalgae for nutrient removal from waste water.

In recent decades, the eutrophication of surface water has become a major environmental concern. Increased concentration of nutrients such as nitrogen and phosphorous lead to eutrophication condition which highlights the demand for effective and economical methods of removing nitrogen and phosphorous from waste water. Bio flocculation using microalgae is an excellent candidate for satisfying the dual purpose of nutrient removal and waste water treatment. It has so many advantages over conventional methods such as toxic free, no chemical is needed, low cost etc. In this review the bio flocculation of microalgae, its mechanisms, applications and harvesting methods are discussed.
 Keywords: Bio flocculation, microalgae, nutrient removal, waste water treatment

Seasonal Mixing and Biological Controls of the Carbonate System in a River-Dominated Continental Shelf Subject to Eutrophication and Hypoxia in the Northern Gulf of Mexico

Large rivers export a large amount of dissolved inorganic carbon (DIC) and nutrients to continental shelves; and subsequent river-to-sea mixing, eutrophication, and seasonal hypoxia (dissolved oxygen < 2 mg⋅L–1) can further modify DIC and nutrient distributions and fluxes. However, quantitative studies of seasonal carbonate variations on shelves are still insufficient. We collected total alkalinity (TA), DIC, and NO3– data from nine cruises conducted between 2006 and 2010 on the northern Gulf of Mexico continental shelf, an area strongly influenced by the Mississippi and Atchafalaya Rivers. We applied a three-end-member model (based on salinity and potential alkalinity) to our data to remove the contribution of physical mixing to DIC and nitrate distribution patterns and to derive the net in situ removal of DIC and nitrate (ΔDIC and ΔNO3–, respectively). Systematic analyses demonstrated that the seasonal net DIC removal in the near-surface water was strong during summer and weak in winter. The peak in net DIC production in the near-bottom, subsurface waters of the inner and middle sections of the shelf occurred between July and September; it was coupled, but with a time lag, to the peak in the net DIC removal that occurred in the near-surface waters in June. A similar 2-month delay (i.e., January vs. November) could also be observed between their minima. A detailed examination of the relationship between ΔDIC and ΔNO3– demonstrates that net biological activity was the dominant factor of DIC removal and addition. Other effects, such as air–sea CO2 gas exchange, wetland exports, CaCO3 precipitation, and a regional variation of the Redfield ratio, were relatively minor. We suggest that the delayed coupling between eutrophic surface and hypoxic bottom waters reported here may also be seen in the carbon and nutrient cycles of other nutrient-rich, river-dominated ocean margins worldwide.

Estimation of Nitrogen Loading to Surface Water from Agriculture Based Area and Its Application for Water Pollution Mitigation

Eutrophication of surface water is a globally widespread environmental problem. Similarly, in Thailand, the Nakhon Nayok River (NNR), located in an agriculture-based area, has been markedly affected by eutrophication problems. However, there are limited studies on significant nitrogen (N) sources during agricultural activities in the area. Therefore, this study examined the major sources and key flows of N loading to the surface water by applying material flow analysis (MFA) to the relevant seven subsystems in 2018. The results showed that aquaculture and rice cultivation were the main sources of nitrogen inputs and outputs. Both considerably contributed to the nitrogen loading to the surface water, yet nitrogen released from the aquaculture was five times higher than the rice cultivation. The nitrogen flux found in the study area was 0.11 kg/ha. Accordingly, creating wetlands for aquaculture wastewater treatment that could potentially remove nitrogen by 12% was recommended.

Coupling Bayesian-Monte Carlo simulations with substance flow analysis for efficient pollutant management: A case study of phosphorus flows in China

Phosphorus is an essential nutrient for plants and also a natural component of healthy rivers. Yet, an overload of phosphorus could lead to the degradation of water quality in rivers and streams, thereby causing eutrophication of surface waters. Substance flow analysis (SFA) as a well-established analytical method has been widely used by scholars and scientists to quantify and manage the major nutrient flows entering water bodies over different spatial scales, e.g., the watershed or regional or national scale. However, despite its utility, this method has a notable limitation in that it cannot quantify the data uncertainty efficiently. This may significantly limit its application and lead to less reliable results. In this study, we propose a conceptual framework which enables integration of Bayesian networks, Monte Carlo simulations and substance flow analysis. The Bayesian-Monte Carlo simulation-based substance flow analysis (BMC-SFA) technique is able to account for random uncertainty, and thus can help to deliver an improved understanding of nutrient flows in surface waters. We use the BMC-SFA technique to carry out a systematic analysis of phosphorus flows in China. The results show that the livestock droppings on farmlands account for the most considerable uncertainty of phosphorus flows in China. Suggestions for uncertainty reduction and risk management are given to enable efficient phosphorus flow management in the future. Overall, the BMC-SFA technique can be a useful tool for guiding pollution control and water quality improvement efforts in surface waters.

Simultaneous removal of nitrate and phosphate in groundwater using Ca-citrate complex.

Eutrophication can be caused by excessive input of nutrients, such as nitrate and phosphate, to surface water. Nutrients in groundwater can enter surface water by means of base flow, requiring treatment before they reach surface water bodies. While some studies have attempted to remove nitrate and phosphate, methods for simultaneous removal in groundwater have rarely been reported. In this study, we propose an innovative treatment method to simultaneously remove nitrate and phosphate in groundwater based on an injection of Ca-citrate complex. A total of five batch experiments with different conditions were conducted to identify the removal mechanisms of nitrate and phosphate and to evaluate the use of alternative organic materials, such as lactate. The results showed that Ca-citrate complex can remove nitrate and phosphate simultaneously. Nitrate was removed through denitrification by denitrifying bacteria which used citrate as a carbon source. The removal mechanisms for phosphate were precipitation of phosphate minerals (e.g., hydroxyapatite) and adsorption. The results also showed that reactive materials based on Ca-lactate complex were able to remove nitrate and phosphate. This study suggests that nitrate and phosphate in groundwater can simultaneously be removed using organic-based calcium complexes, proposing a promising remedial method to alleviate potential eutrophication in surface water as well as groundwater contamination.

Genetic variation of seed phosphorus concentration in winter oilseed rape and development of a NIRS calibration

Phytic acid is the major organic phosphorus storage compound in rapeseed. Following oil extraction, the defatted meal is used in feed mixtures for livestock. However, monogastric pigs and chickens can only poorly metabolize phytate. Hence, their excrements are rich in phosphorus (P), which when applied as manure may lead to eutrophication of surface waters. The aim of the present study was to analyze the genetic variation for total and organic P concentration (i.e. mainly phytate) in rapeseed and to compare the results with soybean. Two sets of rapeseed material were tested in field experiments in different environments with varying soil P levels and harvested seeds were used for seed quality analysis. Results revealed significant genotypic differences in total seed P concentration, which ranged from 0.47 to 0.94%. Depending on the experiment, the heritability for total P concentration ranged from 52 to 93%. The organic P portion of total P concentration was above 90% for current rapeseed hybrids. In both sets, there was a significant positive correlation between seed protein and P concentration. A NIRS calibration for total P concentration in intact seeds showed in cross validation a standard error of 0.05% and a coefficient of determination of R2 = 0.83. Total P concentration of soybean seeds and meal was between 0.55 and 0.65%, and around 1.1% for rapeseed meal. Rapeseed meal had a twofold higher ratio of total P to nitrogen concentration as compared to soybean which could be considered adverse when the meal is used for feeding livestock.

Roles of Phosphate Solubilizing Microorganisms from Managing Soil Phosphorus Deficiency to Mediating Biogeochemical P Cycle.

Simple SummaryPhosphate solubilizing microorganisms (PSMs), a large microflora that mediate bioavailable soil P, play a critical role in soil by mineralizing organic P, solubilizing inorganic P minerals, and storing large amounts of P in biomass. Given that the basic soil P forms and orthophosphate levels can be mediated by PSMs, we conclude that PSMs also play a critical role in the soil P cycle. The present review summarizes the comprehensive and recent understanding about the roles of PSMs in P geochemical processes. Phosphorus (P) is a vital element in biological molecules, and one of the main limiting elements for biomass production as plant-available P represents only a small fraction of total soil P. Increasing global food demand and modern agricultural consumption of P fertilizers could lead to excessive inputs of inorganic P in intensively managed croplands, consequently rising P losses and ongoing eutrophication of surface waters. Despite phosphate solubilizing microorganisms (PSMs) are widely accepted as eco-friendly P fertilizers for increasing agricultural productivity, a comprehensive and deeper understanding of the role of PSMs in P geochemical processes for managing P deficiency has received inadequate attention. In this review, we summarize the basic P forms and their geochemical and biological cycles in soil systems, how PSMs mediate soil P biogeochemical cycles, and the metabolic and enzymatic mechanisms behind these processes. We also highlight the important roles of PSMs in the biogeochemical P cycle and provide perspectives on several environmental issues to prioritize in future PSM applications.

Predicting relative agronomic efficiency of phosphorus-rich organic residues

Relative agronomic efficiency (RAE) of phosphorus (P) in nutrient-rich residues with different chemical characteristics must be known in order to optimize their use as fertilizers, to avoid underfertilization of crops or eutrophication of surface waters due to overfertilization. In this study, we determined the chemical characteristics and RAE of manures (cattle, pig, fox) and sewage sludges subjected to different treatments (anaerobic digestion, composting, lime stabilization, thermal hydrolyzation, pyrolyzation, hydrothermal carbonization (HTC)) by growing barley (Hordeum vulgare, var. Elmeri) to maturity in three independent growth trials. All manures had high RAE (up to 189% in pig slurry), while RAE was only 6–17% for digested and composted sewage sludges when precipitation with Fe used for P removal from wastewater. Pyrolyzation and HTC further depressed RAE to 1–6%. Alternative wastewater treatment processes are therefore needed to increase P recycling potential. For cattle and pig manures and anaerobically digested or composted sewage sludges, molar ratio of (Fe + Al)/P, varying from 0.08 to 2.69, was the best predictor of RAE (R2 = 0.99), with negative correlations with grain yield. Sources in which calcium was more influential for P solubility (fox manure and lime-stabilized sewage sludge) and pyrolyzed and HTC-treated residues did not follow this trend. Conventional extraction methods (2% formic acid, 2% citric acid, neutral ammonium citrate, water and 0.5 M NaHCO3) either underestimated or overestimated RAE of P-rich organic residues, depending on their chemical characteristics.

Water Exchanges and Phosphorus Flux between a Reservoir and Eutrophic Littoral Zone

HighlightsConvective currents led to hydraulic flux and transport of P between bottom and surface waters of the littoral zone.Hydraulic flux was primarily into the bottom of the cove and out of the cove along the surface.Eutrophic littoral areas are a significant source of P to the photic zone of reservoirs, supporting algal growth.Abstract. Eutrophication of surface waters is defined by excessive algal growth, with consequences for drinking water treatment. The sources of phosphorus (P) in southern U.S. reservoirs that fuel peak algal productivity in late summer are still not fully understood. One potential source is reservoir littoral zones, which have been described as the most productive zone of a waterbody. A shallow cove named Granny Hollow in Beaver Lake, northwest Arkansas, was selected as an isolated and semi-controlled location to measure and model sources of P and its transport in a littoral area for the month of July 2018. Hydraulic and P fluxes between the reservoir and littoral area were quantified through field measurements and a 3D lake model. In quantifying hydraulic flux for the month of July, the model indicated that water tended to move into the cove along the bottom and out along the top, with a net hydraulic flux out of the cove of -723,000 m3. Peak surface velocity in the cove averaged 2.09 cm s-1 for the month of July, while peak bottom velocity was 1.29 cm s-1. Diurnally, water movement switched directions, moving out of the cove along the surface during differential heating and into the cove along the surface during differential cooling due to thermoconvective flow. During differential heating, the water velocity and hydraulic flux to the main reservoir channel along the surface of the cove were greater than the velocity and flux in the opposite direction during differential cooling. The sources of P within the cove during July included P released from bottom sediments within the cove and littoral zone and transport of P from the reservoir channel to the cove. Transport of P from the main reservoir into the cove was a result of thermoconvective flow. During differential heating, bottom waters from the main reservoir channel were transported to the surface within the littoral zone by thermoconvective currents flowing upslope from deeper to shallower waters. This resulted in P exchange between the reservoir and littoral area and is significant because it represents movement of P from the bottom of the reservoir upward into the photic zone, where it can be used for algal productivity. During July 2018, it was estimated that 13.3 kg of P were transported from the bottom of the cove to the surface by convective currents and subsequently out of the cove. This study shows that eutrophic coves represent a significant source of P to the reservoir and more importantly to the photic zone, supporting algal growth. Keywords: 3D reservoir model, Eutrophication, Internal loading, Thermoconvective flow.

Nitrogen forms in runoff export from St. Augustinegrass

AbstractNitrogen exports from landscapes can contribute to the eutrophication of surface waters. The most common form of N studied in prior runoff research has been nitrate, although ammoniacal and organic forms of N are also considered important causes of eutrophication. The relative abundance of each N form in runoff from turfgrasses has not been widely reported. The objective of this study was to quantify dissolved inorganic N (DIN) and dissolved organic N (DON) exports in runoff from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf over a 2‐yr period in College Station, TX. Treatments were arranged as a randomized complete block design having eight combinations of irrigation (100, 75, or 50% of estimated turfgrass water requirements) and fertility level (0, 88, and 176 kg N ha−1 yr−1). Runoff from 31 rainfall events and one excess irrigation event were used to estimate annual and seasonal DIN and DON exports. Nitrate‐N concentration was typically below 5 mg L−1, but peaks in excess of 20 mg L−1 were measured during late winter in one year. Aside from this atypical peak, the largest portion of total dissolved N (TDN) was DON, whereas NH4–N was typically the smallest portion. Increasing fertilizer rates typically amplified each form of N in runoff, but NO3–N was the most responsive to N rate, with corresponding reductions in the DON/TDN ratio and increases in the nitrate/ammonium ratio. Nitrate‐N may be the best indicator for fate of anthropogenic N inputs, but studies focusing only on NO3–N are likely underreporting N exports.

Phosphorus removal potential at sewage treatment plants in Bavaria – a case study

Controlling phosphorus emissions from sewage treatment plants is a key factor in preventing eutrophication of surface waters. Regarding surface waters in Germany, the orientation value for the "good ecological status" for total phosphorus (Ptotal) is set at 0.10 mg Ptotal/L. To achieve this value, a further reduction in the Ptotal emissions from sewage treatment plants (STPs) is required. The evaluation of 2,626 Bavarian STPs showed a high reduction potential of the Ptotal emissions in STPs treating more than 1,000 population equivalents (PE). To achieve the goal of improving the surface water quality as well as to investigate which option is most feasible for Bavaria, three alternative scenarios of tightening the discharge permits of Ptotal were considered. By these scenarios, a reduction of the Ptotal load by app. 35%-50% can be achieved. For example, to reduce 50% of the Ptotal load, the discharge permits should be set as follows: STPs from 1,000 to 10,000 PE should comply with 1.0 mg Ptotal/L, STPs >10,000 PE to 0.5 mg Ptotal/L. The required annualized specific capital investment and operating costs required to implement simultaneous precipitation are fluctuating between 2 and 5 €/(PE•y). In larger STPs, an average effluent concentration of 0.5 mg Ptotal/L can generally be achieved, if clarification is designed and operated in accordance with applied regulated designing standards.

Estimation of nitrogen and phosphorus concentrations from water quality surrogates using machine learning in the Tri An Reservoir, Vietnam.

Surface water eutrophication due to excessive nutrients has become a major environmental problem around the world in the past few decades. Among these nutrients, nitrogen and phosphorus are two of the most important harmful cyanobacterial bloom (HCB) drivers. A reliable prediction of these parameters, therefore, is necessary for the management of rivers, lakes, and reservoirs. The aim of this study is to test the suitability of the powerful machine learning (ML) algorithm, random forest (RF), to provide information on water quality parameters for the Tri An Reservoir (TAR). Three species of nitrogen and phosphorus, including nitrite (N-NO2-), nitrate (N-NO3-), and phosphate (P-PO43-), were empirically estimated using the field observation dataset (2009-2014) of six surrogates of total suspended solids (TSS), total dissolved solids (TDS), turbidity, electrical conductivity (EC), chemical oxygen demand (COD), and biochemical oxygen demand (BOD5). Field data measurement showed that water quality in the TAR was eutrophic with an up-trend of N-NO3- and P-PO43- during the study period. The RF regression model was reliable for N-NO2-, N-NO3-, and P-PO43- prediction with a high R2 of 0.812-0.844 for the training phase (2009-2012) and 0.888-0.903 for the validation phase (2013-2014). The results of land use and land cover change (LUCC) revealed that deforestation and shifting agriculture in the upper region of the basin were the major factors increasing nutrient loading in the TAR. Among the meteorological parameters, rainfall pattern was found to be one of the most influential factors in eutrophication, followed by average sunshine hour. Our results are expected to provide an advanced assessment tool for predicting nutrient loading and for giving an early warning of HCB in the TAR.

Stoichiometric relations of C, N, and P in urban top soils in Nanjing, China, and their biogeochemical implications

With increasing urban area and population, global cities are playing a more important role in the alteration of the global biogeochemical cycles. The aims of this study are to understand the concentrations and stoichiometric relations of biogenic elements (C, N, and P) in urban soils, further to reveal the effects of C, N, and P accumulation on the urban environment. We collected 317 surface (0–10 cm) soil samples taken from Nanjing, China, a typical city with more than 2000 years of history. These soil samples were located in different urban zones of Nanjing with different land use histories. The soil C, N, and P concentrations were determined. The stoichiometric relations of soil C, N, and P were investigated in urban soils. Meanwhile, some studies on sources of C, N, and P in diverse urban settings from literature were combined to explore the universal rule of C, N, and P cycling and their ecological and environmental effects in urban area. Compared to rural soils, more C, N, and P are accumulated in the urban soils, which also change their stoichiometric relations. The concentrations of OC, TN, and TP in urban top soils are 17.0 ± 9.69 g kg−1, 1.53 ± 0.92 g kg−1, and 1.31 ± 0.67 g kg−1, respectively. The mean atomic ratio of C:N:P is 37:3:1 in the surface of urban soils that strictly differs from natural soils in China and the whole world. The mean of C:N ratio in urban soils is similar to that of agriculture, grassland, and forest soils. However, the ratios of C:P and N:P in urban soils are much lower than that in agricultural, forest, and grassland soils. This implies that P is extremely enriched in the urban soils. The high C in urban soils are considered coming from natural and anthropogenic sources. The high N and P mainly come from anthropogenic sources. The well-constrained C:N:P ratio in rural soils does not apply for urban soils. The abnormal C:N:P ratio of urban soils is the result of unbalanced accumulation of C, N, and P from human activities. Urban soils are already an important storage of carbon. High N and P in urban soils may bring threat of surface water eutrophication and ground water contamination. These effects are expected to increase with the city development time.

Seasonal changes predominant over manure application in driving dissolved organic matter shifts in agricultural runoff

Non-point source nutrient pollution can cause eutrophication, hypoxic events, and harmful algal blooms in surface waters. Surface water eutrophication is frequently attributed to agricultural runoff, a known source of inorganic and organic nutrients to surface and subsurface waters. Analysis of dissolved organic matter (DOM) using ultrahigh resolution mass spectrometry is an effective tool for characterizing diverse organic nitrogen and phosphorus components of DOM that may be mineralized and/or assimilated and ultimately contribute to eutrophication. An anion exchange resin was applied to extract DOM from surface and subsurface tile runoff from agricultural plots located within the Maumee River watershed (Ohio, USA) that received raw liquid manure, polymer-treated dewatered manure, or no manure (control). DOM extracts were analyzed using Fourier transform ion cyclotron resonance mass spectrometry prior to manure application and during three runoff events after manure application. Organic nitrogen compounds were predominant, making up 38–48% of the total assigned formulas. Principle coordinates analysis indicated clustering predominately by sample month and secondarily by treatment. These findings show that a large amount of variability in DOM in runoff was observed regardless of manure application, indicating the important role played by natural processes in driving transformation of the DOM pool during the growing season. Molecular ions unique to runoff from manure-applied plots were also identified that may be useful in source-tracking of non-point source nutrient pollution in waters draining to Lake Erie.

Evaluation of phosphate adsorption by porous strong base anion exchangers having hydroxyethyl substituents: kinetics, equilibrium, and thermodynamics.

Phosphate anions are recognized as the main responsible for the eutrophication of surface waters. In this work, two strong base anion exchangers having either N,N-dimethyl 2-hydroxyethylammonium (SBAEx.2M) or N,N-diethyl 2-hydroxyethylammonium (SBAEx.2E) functional groups, as highly efficient sorbents in the removal of phosphate anions, are presented. The influence of the main parameters (pH, contact time, initial concentration of phosphate, temperature) on the adsorption performances was investigated in batch mode. Modeling the kinetics data by Lagergren, Ho and McKay, and Elovich kinetic models indicated chemisorption as the main mechanism of sorption. The sorption at equilibrium was modeled with Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherm models. The experimental isotherms were the best fitted by Langmuir and Sips isotherms, the maximum sorption capacity for phosphate anions being 233.88 mg g-1 SBAEx.2M and 223.5 mg g-1 SBAEx.2E, at pH 3, and 23 °C. Adsorption of phosphate anions in competitive conditions showed that the interference with co-existing anions was low in the case of Cl- ions and much higher with SO42- ions, the ion exchange having an important contribution in the adsorption process. The adsorption was spontaneous and endothermic, the degree of spontaneity increasing with the increase of temperature. The high level of reusability, the adsorption capacity decreasing with only ~ 7% in the case of SBAEx.2E and with ~ 9% in the case of SBAEx.2M, after five sorption/desorption cycles, recommends these SBAEx as promising adsorbents for phosphate removal.

Benthic Respiration in Hypoxic Waters Enhances Bottom Water Acidification in the Northern Gulf of Mexico

AbstractIt is known that surface water eutrophication enhances bottom water ocean acidification via respiration in coastal oceans. However, the role of benthic processes in influencing bottom water acidification has not been sufficiently explored. We examined this issue by analyzing a 10‐year summer carbonate chemistry dataset in bottom water together with recent benthic flux measurements and literature benthic flux data in the northern Gulf of Mexico. The difference between the observed and estimated pH (Ω) values calculated from anthropogenic CO2 increase and water column aerobic respiration were defined as ΔpH (ΔΩ). We found that ΔpH and ΔΩ values in hypoxic condition were −0.03 ± 0.04 (mean ± standard deviation) and −0.15 ± 0.39, respectively. Both ΔpH and ΔΩ values in hypoxic conditions were significantly lower than zero (p < 0.05). The net results of anaerobic respiration, oxidation of reduced chemcials, burial of iron sulfide minerals, and possible CaCO3 dissolution may have led to an alkalinity to DIC production ratio of less than 1 in porewater. This caused the ratio of alkalinity to dissolved inorganic carbon fluxes from sediment to bottom water to be less than 1, which led to additional bottom water acidification. Our analysis and model simulations demonstrate that severe hypoxic and anoxic conditions, which correspond to less water movement, favor the accumulation of benthic respiration products, leading to additional pH and Ω reductions. The findings on sediment processes contributing to acidification in bottom waters provide new insights into the sensitivity of coastal ocean acidification to low‐oxygen conditions under current and future climates and anthropogenic nutrient loading scenarios.

Temporal and spatial trends of a floating islands system’s efficiency

Floating Treatment Systems (FTWs) are known to be an efficient means to treat eutrophic surface waters, but most of the studies are related to the use of FTWs at the laboratory, microcosm or mesocosm level. It is necessary to expand these studies to larger surface areas and to introduce new supporting materials, substrates and plants adapted to the different regional conditions. This study aimed to evaluate the efficiency of temporal and spatial remediation of a floating island system, set up in a 400m2 experimental area delimited in an urban reservoir located on the main campus of the Federal University of Campina Grande-PB, Brazil. The experiment was carried out in three stages and 16 physicochemical and biological variables were monitored at thirteen sampling points regularly distributed in the study area, for a period of eight months. Temporally, the variables turbidity, electrical conductivity and total, fixed and volatile dissolved solids tended to decrease. Spatially, considering the 13 sampling points in sequence, the trend of reductions were found in the total dissolved solids, volatile dissolved solids and electrical conductivity. The trend of elevation was more substantial for the concentrations of ammonia-nitrogen and orthophosphate. In addition, occasional substantial reductions was found in variables that did not show statistical trends, such as chemical oxygen demand and total phosphorus. This study demonstrated the importance of expanding the scale of evaluation of floating island systems, finding significant results in terms of reduction of pollutants and adaptation of new structures and plants to adverse environmental conditions.

What evidence exists related to soil retention of phosphorus from on-site wastewater treatment systems in boreal and temperate climate zones? A systematic map protocol

BackgroundSoil-based on-site wastewater treatment systems (OWSs) are suspected to contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). However, along the flow path between the facilities and surface waters, different processes contribute to delay the transport of phosphorus through the ground. This may reduce the unwanted impact on receiving water bodies. However, the strength and significance of this so-called soil retention remains unclear.In Sweden, there are nearly one million OWSs. To protect surface waters, a high P removal rate (up to 90%) is often required by the local municipalities. However, since these requirements may have costly consequences to property owners, it is debated as to whether they are too strict. In this debate, it is often claimed that the retention of P occurring in natural environments may be underestimated by authorities. Accordingly, there is a need for a scrutiny of the available evidence related to soil retention of phosphorus from OWSs. This is the objective of the planned systematic map. Focus will be on boreal and temperate climate zones.MethodsSearches will be made for peer-reviewed articles and grey literature using bibliographic databases, search engines, specialist websites and stakeholder contacts. The references will be screened for relevance according to a predefined set of eligibility criteria. At stage one, after testing and clarifying the eligibility criteria, the references will be single-screened based on title and abstract. At stage two, potentially relevant references will be screened in full-text independently by two reviewers. We will compile a detailed database of the relevant studies. Moreover, a narrative report will be produced, describing the research landscape in general terms. This will be carried out with a conceptual model, describing the processes involved in P retention in natural environments, as a foundation. It will be discussed where the respective studies/study types fit into the conceptual model, and also evaluated how each study/study type can be related to the overarching question of eutrophication. Moreover, we will describe identified knowledge gaps that warrant further primary research effort, as well as identified knowledge clusters that could be suitable for systematic reviews.

The control of point and non-point source nitrogen to prevent eutrophication of the Nakdong River basin, Korea

Eutrophication of surface waters is commonly caused by excessive inputs of nutrients such as nitrogen and phosphorus. Nakdong River basin was chosen as the study area to investigate the effect of point and non-point source pollution of nitrogen on eutrophication in water body. Non-point source inputs of nitrogen accounted for approximately 84% in the total nitrogen input of the upper Nakdong river watershed, which mainly consists of agricultural land and forests. However, point source inputs of nitrogen accounted for 58~85% in the total nitrogen input of the middle and lower watersheds, including urban area. Therefore, for watershed near urban area, control of point source inputs of nitrogen may be an optimal method to control eutrophication. In this respect, the enforcing reduction of nitrogen in the final effluent of wastewater treatment facilities is needed. On the other hand, to enact more stringent nitrogen regulations, the LOT (limit of technology) and environmental impact should be considered. In this study nitrogen data were analyzed to propose new nitrogen regulations.

Full-scale thermophilic aerobic co-composting of blue-green algae sludge with livestock faeces and straw

A high incidence of harmful algal bloom in eutrophic surface waters causes many environmental problems. Thermophilic aerobic composting enables effective treatment and disposal of algal sludge that remains after the dewatering of algae slurries, and provides a value-added organic fertiliser. Previous studies have either only dealt with the composting of a single waste component or were conducted at a lab-/pilot-scale; however, this work is a comprehensive assessment of full-scale mechanized thermophilic aerobic co-composting of algal sludge and other typical biomass-based wastes, including chicken faeces and rice straw, in a water-rich rural area in the Tai lake basin, China. With the optimised feedstock material mass ratio (6.0:1.8:1.0 for straw:algae:faeces; initial C/N ratio of 20; and initial moisture of 60 wt%), the co-composting process effectively achieved the reduction, harmlessness, and reuse of waste. The moisture content (28.36 wt% of wet weight), organic matter content (57.91 wt% of dried weight), total nutrient content (6.59 wt% for TN + TP + TK of dried weight), and heavy metal contents as well as the pH of the final product fully met the Chinese National Agricultural Organic Fertiliser Standard requirements. The reduction rates of microcystin and toxic volatile fatty acid contents were higher than 99.5%, and the seed germination index of the product was 114.5%. A notable economic benefit with a gross profit margin of 167–434% of the process was highlighted. Investigation of the associated mechanisms, including statistical analysis, spectral characterisation, micro-morphological observation, and microbial community analysis, revealed that a decreased particle sizes with a looser structure and an efficient humification effect, resulting from the work of several identified dominant microbial species, contributed to the high product quality. The current study provided a demonstration of the promising full-scale co-composting technology for comprehensive management of the environment in water-rich rural areas and the construction of a sustainable watershed.