Biofiltration Process Research Articles

Relative abundance and the fate of human rotavirus in wastewater during treatment processes: identification of potential infectious rotavirus in the final effluents and receiving aquatic milieu in Durban area, South Africa

The occurrence and persistence of rotaviruses in raw and treated wastewater and their discharge into rivers represent a significant health risk for humans and animals, worldwide. In this study, samples were collected monthly from each of the four Durban wastewater treatment plants (DWWTPs) and receiving rivers for a period of 3 months. Rotavirus was quantified by real-time quantitative PCR (RT-qPCR), and viability was assessed using integrated cell culture (ICC)-qPCR. Rotavirus was detected consistently in 100% of influent wastewaters (mean concentration range, 4.36–4.46 log10 genome equivalent (GE) copies/L) and final effluent samples of three DWWTPs (range, 3.35–3.61 log10 GE copies/L). Overall, 94% (45/48) of the wastewater analyzed and 95% (20/21) of the associated river water samples were positive for rotavirus (range, 2.04–6.77 log10 GE copies/L). The activated sludge process with 0.10–0.43 log10 reduction values (LRV) only moderately reduced the viral loads. Similarly, one of the DWWTPs that operated the biofilter modality produced 0.20 LRV. Though the additional treatment with chlorine produced higher LRV (range, 0.31–0.53) than the corresponding activated sludge or biofilter process, the difference in viral removals was not significant (p > 0.05). The equivalent treatment efficiencies of the four DWWTPs varied from 19 to 43% decay in the population of rotavirus. Further, infectious rotavirus ranging from 66.67 to 100%, 50 to 100%, and 66.67 to 100% were detected in the post-activated sludge, final effluents, and river water samples, respectively. In conclusion, the findings of infectious rotavirus in both the final effluents and associated rivers represent an infection risk for humans or animals during contact. Thus, close monitoring for rotavirus and risk assessment studies under distinct exposure scenarios may further shed light on the health-related risks associated with water recovery and reuse in urban settings.

Biodegradation kinetics of organic micropollutants in biofilters for advanced wastewater treatment – Impact of operational conditions and biomass origin on removal

Biofiltration processes are often part of advanced wastewater treatment (aWWT) technologies for the removal of organic micropollutants (OMP) from conventional wastewater treatment plant (WWTP) effluents. Although biological effects are not always the main focus of these technologies (e.g. filtration through granular activated carbon), they have been shown to contribute significantly to total OMP removal. While OMP biodegradation kinetics in conventional biological wastewater treatment are well researched, no systematic comparison to biomass from aWWT is available. This biomass faces different growth conditions and higher OMP concentrations relative to the background organic matter. Adaptation to these conditions could be possible and could lead to faster OMP biodegradation kinetics, which would show in a larger pseudo first-order biodegradation kinetic constant kbiol. In this work, kbiol values for biomass obtained from aWWT biofilters were determined by evaluating OMP removals measured in lab-scale biofilters using a mechanistic model of the experimental setup. A comparison to kbiol values from literature for conventional wastewater treatment (with nutrient removal) revealed similar OMP biodegradation kinetics without any advantages of biomass from aWWT. A conceptual evaluation of influencing factors on OMP removal in biofilters showed that operational parameters (such as the biomass concentration or the empty bed contact time) and the affinity of OMPs to adsorb on biomass have a significant additional effect on biological OMP removal. Therefore, kbiol values alone are not sufficient to estimate biological OMP removal in biofilters and further information about the system is required.

Linking Pattern Shifts of Dissolved Organic Nitrogen Fractional Removal with Microbial Species Richness in a Cascade Upflow Biofiltration Process

Nutrient pollution has become an important issue to solve in stormwater runoff due to the fast population growth and urbanization that impacts water quality and triggers harmful algal blooms. There is an acute need to link the dissolved organic nitrogen (DON) decomposition with the coupled nitrification and denitrification pathways to realize the pattern shifts in the nitrogen cycle. This paper presented a lab-scale cascade upflow biofiltration system for comparison of nitrate and phosphate removal from stormwater matrices through two specialty adsorbents at three influent conditions. The two specialty adsorbents are denoted as biochar iron and perlite integrated green environmental media (BIPGEM) and zero-valent iron and perlite-based green environmental media (ZIPGEM). An initial condition with stormwater runoff, a second condition with spiked nitrate, and a third condition with spiked nitrate and phosphate were used in this study. To differentiate nitrifier and denitrifier population dynamics associated with the decomposition of DON, integrative analysis of quantitative polymerase chain reaction (qPCR) and 21 tesla Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were performed in association with nitrate removal efficiencies for both media with or without the presence of phosphate. While the qPCR may detect one gene for a single microbe or pathogen and realize the microbial population dynamics in the bioreactors, the 21 T FT-ICR MS can separate and assign elemental compositions to identify organic compounds of DON. Results indicated that ZIPGEM obtained a higher potential for nutrient removal than BIPGEM when the influent was spiked with nitrate and phosphate simultaneously. The sustainable, scalable, and adaptable upflow bioreactors operated in sequence (in a cascade mode) can be expanded flexibly on an as-needed basis to meet the local water quality standards showing process reliability, resilience, and sustainability simultaneously.

A Circular Bioeconomy Approach to Using Post-Bioadsorbent Materials Intended for the Removal of Domestic Wastewater Contaminants as Potential Reinforcements.

Agro-industrial residue valorization under the umbrella of the circular bioeconomy (CBE) has prompted the search for further forward-thinking alternatives that encourage the mitigation of the industry's environmental footprint. From this perspective, second-life valorization (viz., thermoplastic composites) has been explored for agro-industrial waste (viz., oil palm empty fruit bunch fibers, OPEFBFs) that has already been used previously in other circular applications (viz., the removal of domestic wastewater contaminants). Particularly, this ongoing study evaluated the performance of raw residues (R-OPEFBFs) within three different size ranges (250-425, 425-600, 600-800 µm) both before and after their utilization in biofiltration processes (as post-adsorbents, P-OPEFBFs) to reinforce a polymer matrix of acrylic resin. The research examined the changes in R-OPEFBF composition and morphology caused by microorganisms in the biofilters and their impact on the mechanical properties of the composites. Smaller R-OPEFBFs (250-425 µm) demonstrated superior mechanical performance. Additionally, the composites with P-OPEFBFs displayed significant enhancements in their mechanical properties (3.9-40.3%) compared to those with R-OPEFBFs. The combination of the three fiber sizes improved the mechanical behavior of the composites, indicating the potential for both R-OPEFBFs and P-OPEFBFs as reinforcement materials in composite applications.

Synergistic Biofilter Tube for Promoting Scarless Tendon Regeneration.

Inspired by the imbalance between extrinsic and intrinsic tendon healing, this study fabricated a new biofilter scaffold with a hierarchical structure based on a melt electrowriting technique. The outer multilayered fibrous structure with connected porous characteristics provides a novel passageway for vascularization and isolates the penetration of scar fibers, which can be referred to as a biofilter process. In vitro experiments found that the porous architecture in the outer layer can effectively prevent cell infiltration, whereas the aligned fibers in the inner layer can promote cell recruitment and growth, as well as the expression of tendon-associated proteins in a simulated friction condition. It was shown in vivo that the biofilter process could promote tendon healing and reduce scar invasion. Herein, this novel strategy indicates great potential to design new biomaterials for balancing extrinsic and intrinsic healing and realizing scarless tendon healing.

Penyisihan Kandungan Perak dalam Limbah Cair Pencucian Film Melalui Proses Biofiltrasi dengan Tanaman Eceng Gondok

Wastewater produced from the film washing process in photo studios generally has very high contents of heavy metals, such as silver (Ag). This situation can cause various health and environmental problems if it is not treated before disposal. Therefore, this research was aimed to reduce the silver content in the wastewater through biological processes. This study was conducted using a biofiltration process using water hyacinth plants. Film washing waste was first acclimatized into concentration of 2.5% and the initial silver content was measured. Afterwards, water hyacinth of 600, 900, 1200, and 1500 g, respectively, was planted into the wastewater. Waste samples were subsequently taken and analyzed every 2 days. The highest removal efficiency of 99.94% was yielded for 1500 g of plant. In this condition, the silver content in wastewater met the environmental quality standards.

Simultaneous Removal of Toxic Ammonia (NH3/NH4 +) from Aqueous Solutions Using New Geomaterial Adsorbent: Application to Aquaculture Effluents

This study evaluates the performance of a new geomaterial (GEOM) based on sodium montmorillonite clay (Na-Mt), local activated carbon (CAC) and fine powder local cement (Chlef plant western Algeria) to remove ammonia from fish farming in a recirculating aquaculture system. The aqueous ammonium (NH4 +/NH3) adsorption efficiency of GEOM was compared with its two principals` constituents (Na-Mt and CAC) and another commercial activated carbon (CAG). The results of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to assess the chemical and physicochemical properties of studied adsorbents. The maximum adsorption capacity of NH4 + on GEOM of about 15.57 mg. g-1 seems to be similar to that of Na-Mt 16.82 mg. g-1. The study of solution pH showed that the best NH4 +/NH3 removal efficiency was at pH=6 for both GEOM and Na-Mt. The efficiency of GEOM for ammoniacal nitrogen (NH4 +/NH3) removal was 79.3% in ultrapure water, 94.05% in seawater and 97.5% in real aquaculture wastewater. Thus, the proposed material, GEOM, can be used as a filter material in a bio-filtration process to treat aquaculture wastewater in a real-world context.

The Influence of the Biofiltration Method on the Efficiency of Ammonium Nitrogen Removal from Water in Combined Sorption and Nitrification Processes

This study assessed the impact of the method of conducting the biofiltration process on the efficiency of ammonium nitrogen removal from water in combined sorption and nitrification processes. The research was carried out on diatomite deposits using biofiltration with gravity and counter-gravity flow. The following physicochemical water parameters were controlled during the research, including ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, and dissolved oxygen. Unconventional flow turned out to be more beneficial because it allows for optimal use of the entire bed surface, natural regulation of the biofilm thickness, and maintaining constant microbiological activity of the biofilm. The automatic regulation of the biofilm thickness during water flow prevented excessive growth of dead organic matter and limited the development of heterotrophic bacteria. Biofiltration with counter-gravity flow also resulted in reduced oxygen consumption. Regardless of the flow direction used, water after the single-stage biofiltration process was characterized by an increased content of nitrite nitrogen. The introduction of the second stage of filtration made it possible to obtain water that meets the requirements for water intended for human consumption.

Methane Biofiltration Processes: A Summary of Biotic and Abiotic Factors

The ongoing yearly rise in worldwide methane (CH4) emissions is mostly due to human activities. Nevertheless, since over half of these emissions are scattered and have a concentration of less than 3% (v/v), traditional physical–chemical methods are not very effective in reducing them. In this context, biotechnologies like biofiltration using methane-consuming bacteria, also known as methanotrophs, offer a cost-efficient and practical approach to addressing diffuse CH4 emissions. The present review describes recent findings in biofiltration processes as one of the earliest biotechnologies for treating polluted air. Specifically, impacts of biotic (such as cooperation between methanotrophs and non-methanotrophic bacteria and fungi) and abiotic factors (such as temperature, salinity, and moisture) that influence CH4 biofiltration were compiled. Understanding the processes of methanogenesis and methanotrophy holds significant importance in the development of innovative agricultural practices and industrial procedures that contribute to a more favourable equilibrium of greenhouse gases. The integration of advanced genetic analyses can enable holistic approaches for unravelling the potential of biological systems for methane mitigation. This study pioneers a holistic approach to unravelling the biopotential of methanotrophs, offering unprecedented avenues for biotechnological applications.

Deodorizing bacterial consortium: community analysis of biofilms and leachate water collected from an air biofiltration system in a piggery.

Intensive livestock production is a source of water, soil, and air contamination. The first aspect that negatively affects the quality of life of residents in the vicinity of piggeries is malodorous aerosols, which are not only responsible for discomfort but can be an etiological factor in the development of various diseases during prolonged exposure. One of the proven and efficient ways to counteract odor emissions is the usage of air biofiltration. The purpose of this study was to qualitatively analyze the bacterial community colonizing the biofilm of a biofilter operating at an industrial piggery in Switzerland. The study material consisted of biofilm and leachate water samples. The microbiological analysis consisted of DNA isolation, amplification of the bacterial 16S rRNA gene fragment (V3-V4), preparation of a library for high-throughput sequencing, high-throughput NGS sequencing, filtering of the obtained sequencing reads, and evaluation of the species composition in the studied samples. The investigation revealed the presence of the following bacterial genera: Pseudochelatococcus, Methyloversatilis, Flexilinea, Deviosia, Chryseobacterium, Kribbia, Leadbetterella, Corynebacterium, Flavobacterium, Xantobacter, Tessaracoccus, Staphylococcus, Thiobacillus, Enhydrobacter, Proteiniclasticum, and Giesbergeria. Analysis of the microbial composition of biofilters provides the opportunity to improve the biofiltration process.

Treatment of domestic effluents using sustainable biofilter methods

The discharge of effluents is a permanent environmental and sanitation concern. Efficient water management must include water treatment and reuse. It is therefore necessary to study treatment systems to improve their performance throughout the entire chain, from drinking water to wastewater or, more specifically, waste effluent. Currently, technologies using bio-filtration processes have proven to be an effective and low-cost method for treating industrial effluents and domestic sewage. In this study, a low-cost domestic sewage treatment system made up of biofilters and pipes was built on a bench model as a means of teaching practical classes, and its efficiency was also studied. The results showed that the equipment can be made from recyclable material and is low-cost, easy to detail technically and easy to handle and operate. The students involved can easily replicate the technology in their communities, thus spreading low-cost sanitation treatment technologies to low-income populations without access to conventional sanitation systems. The parameters pH, turbidity, chlorination, temperature, and electrical conductivity were all at acceptable levels for discharge into receiving bodies and domestic use.

Effect of inoculum type, packing material and operational conditions on the biofiltration of a mixture of hydrophobic volatile organic compounds in air

The emission of volatile organic compounds (VOCs) into the atmosphere causes negative environmental and health effects. Biofiltration is known to be an efficient and cost-effective treatment technology for the removal of VOCs in waste gas streams. However, little is known on the removal of VOC mixtures and the effect of operational conditions, particularly for hydrophobic VOCs, and on the microbial populations governing the biofiltration process. In this study, we evaluated the effect of inoculum type (acclimated activated sludge (A-AS) versus Rhodococcus erythropolis) and packing material (mixture of compost and wood chips (C + WC) versus expanded perlite) on the removal of a mixture of hydrophobic VOCs (toluene, cyclohexane and hexane) in three biofilters (BFs), i.e., BF1: C + WC and R. erythropolis; BF2: C + WC and A-AS; and BF3: expanded perlite and R. erythropolis. The BFs were operated for 374 days at varying inlet loads (ILs) and empty bed residence times (EBRTs). The results showed that the VOCs were removed in the following order: toluene > cyclohexane > hexane, which corresponds to their air-water partitioning coefficient and thus bioavailability of each VOC. Toluene is the most hydrophilic VOC, while hexane is the most hydrophobic. BF2 outperformed BF1 and BF3 in each operational phase, with average maximum elimination capacities (ECmax) of 21 ± 3 g toluene m−3 h−1 (removal efficiency (RE): 100 %; EBRT: 82 s), 11 ± 2 g cyclohexane m−3 h−1 (RE: 86 ± 6 %; EBRT: 163 s) and 6.2 ± 0.9 g hexane m−3 h−1 (RE: 96 ± 4 %; EBRT: 245 s). Microbial analysis showed that despite having different inocula, the genera Rhodococcus, Mycobacterium and/or Pseudonocardia dominated in all BFs but at different relative abundances. This study provides new insights into the removal of difficult-to-degrade VOC mixtures with limited research to date on biofiltration.

Methane biofiltration for the treatment of a simulated diluted biogas emission containing ammonia and hydrogen sulfide

Fugitive methane emissions impair the physical and chemical stability of the atmosphere. Biological systems, such as biofilters, have been proposed as a feasible technology for the abatement of CH4 in diluted emissions (<5% [CH4]). Other gases, such as NH3 and H2S, are also present in these emissions; and they could be detrimental for the performance of biological CH4 abatement strategies. The objective of this work was to establish the magnitude of the impact on the biofiltration of CH4 due to the presence of NH3 and H2S.A methane biofiltration system operating at load of 10 gCH4m-3h−1 was affected by the presence of NH3 and H2S in a synthetic diffuse stream, where the elimination capacity (5.5 gCH4m-3h−1) and efficiency (55%) varied significantly. A combination of 100 ppmv of NH3 and 100 ppmv of H2S decreased the capacity by 17% with respect to the unexposed biofilter while 500 ppmv of NH3 and 300 ppmv of H2S shrink the capacity by 26%. Separately, H2S decreased the methane elimination capacity by 11% under 150 ppmv and 20% when 300 ppmv was supplied. In the case of NH3, the presence of 100 ppmv and 300 ppmv of NH3 increases the methane elimination capacity by 35% and 16%, respectively. A reduction of 32% in the elimination capacity was observed under 1000 ppmv of NH3. We contribute with numerical evidence by which methane biofiltration was affected by secondary gases on a concentration range similar to those in waste methane diffuse stream, establishing the concentration ranges of H2S and NH3 at which it is possible to optimize the process of methane biofiltration and under which performance could be reduced.

Mathematical modelling of the biofiltration treating mixtures of toluene and N-propanol in the biofilm and gas phase

This paper presents a mathematical model in the biofilm phase and in the gas phase that has been successfully applied to investigate various aspects of the biofiltration process. The mixtures of volatile organic compounds (VOCs) are emitted from a wide range of industries, such as chemical, petrochemical, pharmaceutical, pulp paper mills, printing and paint workshops, etc. The objective of the present study is, presence of high n-propanol loading negatively affected the toluene removal; however, n-propanol removal was not affected by the presence of toluene and was effectively removed in the biofilter despite high toluene loadings. A model for toluene and n-propanol biofiltration could predict the cross-inhibition effect of n-propanol on toluene removal. Further, we studied the effects of many physical and biological parameters on model prediction. The mathematical equations (2.12)-(2.16) which are non-linear partial differential equations are solved by using the homotopy perturbation technique. Also, we derived the semi-analytical results for toluene and n -propanol concentrations for saturated and unsaturated kinetics. It is verified that the proposed solution is validated by comparing it with numerical solutions.

Selection of Wastewater Treatment Technology: AHP Method in Multi-Criteria Decision Making

Wastewater treatment is a process that reduces pollution to those quantities and concentrations at which purified wastewater is no longer a threat to human and animal health and safety and does not cause unwanted changes in the environment. Municipal wastewater is classified as biodegradable water. Special importance should be given to wastewater with a high content of organic matter (COD), phosphorus (P) and nitrogen (N). MBBR technology, developed on the basis of the conventional activated sludge process and the bio filter process, does not take up much space and does not have problems with activated sludge, as in the case of conventional biological reactors, and has shown good results for the removal of organic matter, phosphorus and nitrogen. The aim of this paper is to optimize the wastewater treatment process in the municipality of Dojran, North Macedonia. Three alternative solutions for improving the capacity for wastewater treatment in the municipality of Dojran were analyzed. The shortlist of variants was made on the basis of several criteria, including: analysis of the system in the tourist season and beyond, assessment of the condition and efficiency of the existing wastewater treatment plant (WWTP) in combination with a new treatment plant, treatment efficiency when using different wastewater treatment technologies, the size of the site needed to accommodate the capacity, as well as the financial parameters for the proposed system. The selection of the most favorable solution for the improvement of the wastewater treatment system was made using the AHP (analytic hierarchy process) method. In order to select the optimal solution, a detailed analysis was conducted, considering several decision-making criteria, namely the initial investment, operating costs and management complexity. Based on the obtained results, Variant 3 was recommended, that is, the construction of a completely new station with MBBR technology, with a capacity for 6000 equivalent inhabitants.

Influence of Water Treatment Technology on the Stability of Tap Water

Control of water quality changes in the distribution system is an important issue, due to consumer health, and a threat to technical infrastructure. Annual monitoring of water quality allowed us to analyze the physical, chemical, and biological stability of water produced in two different technological systems. The article examines the extent to which water purification technology affects the possibility of uncontrolled changes in water quality during its transport to the consumer (the risk of secondary water pollution has been estimated). Based on the obtained results, it was found that the groundwater treatment system based on the following processes—aeration, coagulation, sedimentation, filtration, and disinfection—does not ensure the effective elimination of biogenic substances that determine sanitary safety. The treatment technology extended by an additional biofiltration process on granulated activated carbons (GAC) contributed to the improvement of the quality of the treated water (lowering the content of nutrients) and reduced the risk of losing the biological stability of the water in the distribution system. The biofiltration process did not change the physical and chemical stability of the water; the calculated corrosiveness indicators showed that the waters are devoid of aggressive properties, with a tendency to precipitate CaCO3. The production of stable water is a step forward in controlling water quality from source to tap.

Management proposal of a naturally occurring wetland modeled as a constructed wetland

Environmental management and restoration aim to accelerate the recovery of ecosystems that have been affected by human activities. This paper presents the diagnosis and management proposal for the Valsequillo wetland, Puebla, Mexico. The study site is a natural wetland dominated by water hyacinth (Eichhornia crassipes) which performs a biofiltration process by reducing the pollutant load of the water. To increase the efficiency of the wetland, an annual harvest plan is proposed in this work. However, the ideal amount of biomass to harvest is unknown. In order determine the optimal annual harvest plan, this natural wetland was modeled as if it were a surface flow wetland by using the equations described. A total of 48 surface water samples were collected in three different seasons of the year (dry, rainy, and winter) and 34 water quality physicochemical parameters were measured. Additionally, two water quality indices were determined, namely: Overall Index Pollution (OIP) and Heavy Metal Evaluation Index (HEI) to determine the degree of contamination in different zones of the study area. The model results showed that in order to achieve the desired removal of total phosphorus (TP) or chemical oxygen demand (COD), 274 ha or 306 ha of aquatic plants must be harvested, respectively. The results of the modeling showed that this action will optimize the function of the wetland by improving the removal of total suspended solids (TSS, 6%), total nitrogen (TN, 24%) TP (31%), chemical oxygen demand (COD, 11%) and biochemical oxygen demand (BOD5, 101%).

Biofiltration Process for Treatment of Water and Wastewater

Biofiltration Process for Treatment of Water and Wastewater

A mixed agro-waste based biofilter for the removal of methyl ethyl ketone: Kinetics and modeling

Biofiltration has grown worldwide, as an inexpensive and consistent air pollution control technology for the elimination of numerous organic compounds. In this work, the biofiltration of methyl ethyl ketone (MEK) has been studied. The agro-wastes namely pressmud and cornstack are mixed and used as packing materials for the removal of MEK. The performance of the biofilter has been explored over 200 days. Experiments are carried out in four periods. In every period, the biofiltration of pollutants is performed for various inlet concentrations (IC) of MEK (0.2–1.2 g m−3) and gas flow rates (GFR) (0.03 m3 h−1 to 0.12 m3 h−1). The biofilter performances are investigated by their removal rates, elimination capacity, temperature, pressure drop, carbon dioxide production, and variation of bed height at the time of operations. For the IC of 0.2 ± 10% g m−3 and GFR of 0.03 m3 h−1, the removal efficiency (RE) of MEK is 97% using the mixture of cornstack (80%) and pressmud (20%). The MEK removal efficiency decreases, when the cornstack ratio increases. The maximum RE is obtained at the IC of 1.2 g m−3 and GFR of 0.12 m3 h−1 for all the tested conditions. The pressure drop (PD) is also measured for all the operating conditions. It is found that the PD rises with an increase in height. The temperature is monitored throughout the biofiltration process. It is observed that an increase in RE leads to a rise in temperature in the biofilter. SEM images confirm the growth of microbes on the packing material. The kinetics of removal of MEK is investigated by using Ottengraf–van den Oever model.

Comparison of urban stormwater plant biofilter designs for nutrient and metal removal in South Africa

Abstract This paper presents a comparison of six plant biofilter designs for urban stormwater quality improvement and reports on their performances. Thirty-six columns were populated with the endemic South African plant Prionium serratum, representing plant biofilter designs that incorporate different pollutant removal mechanisms in the biofiltration process. The experimental biofilter columns were subjected to low, typically observed and high urban nutrient and metal synthetic stormwater pollution for five months. Significant loads of NH3-N and dissolved Cd, Pb and Zn were removed, whereas removal of -N, -P and dissolved Cu was more variable. The most efficient design was found to include standard plant biofiltration techniques with upflow filtration, plenum aeration and a saturated zone supporting anaerobic microbial activity. It was found that the most efficient design removed on average 96% of urban stormwater nutrient and metal loads.