Application Of Treated Wastewater Research Articles

Quantitative and qualitative management of water resources with the use of treated wastewater in agriculture.

The principled utilization of treated wastewater can reduce the pollution load on the environment. Because on the one hand, treated wastewater can be a suitable fertilizer substitute, and on the other hand, using treated wastewater in irrigation prevents the discharge of polluted surface water into water sources. In the south of Tehran province, polluted surface water is used for irrigation in the agricultural sector, and this has led to environmental problems. To solve this problem, it has been decided to implement a plan to build surface water treatment plants and an irrigation and drainage network to transfer treated wastewater to farms. Therefore, the present study aimed to investigate the economic and environmental effects of this project in the region. A hydro-economic model has been used to achieve this goal. According to the results, in the case of the application of environmental constraints in the optimization model, the cultivation area and the farmers' profit will be reduced by about 5% and 36%, respectively, compared with the noncompliance of environmental constraints. However, this decline in profit can be compensated by adopting solutions such as improving the irrigation system, the application of treated wastewater, or using the fertilizer potential of water sources in the agricultural sector. PRACTITIONER POINTS: In the optimal economic-environmental situation, farmers' profit is reduced compared with the optimal economic situation. In the case of implementing the treated wastewater application, the farmers' profit will increase despite environmental constraints. In the optimal economic-environmental situation, fewer lands are cultivated with diverse crops than in optimal economic conditions.

Changes in soil hydraulic and physio-chemical properties under treated wastewater irrigation: A meta-analysis

Treated wastewater (TWW) is increasingly used for irrigation, but its higher salt content compared to conventional water sources can induce soil salinization and sodification. This, in turn, may result in structural degradation and deterioration of soil hydraulic properties. The practice of using TWW for irrigation is not new, and it has long been applied in arid countries, with limited other water resources, while in recent years it is also getting used elsewhere given the worldwide influence on water resources. However, comparing and extrapolating results from existing studies on the use of TWW for irrigation is challenging due to the heterogeneity between experimental setups in terms of water quality, irrigation techniques applied, and pedo-climatic conditions. To explore the effect of TWW quality on soil hydraulic and physio-chemical following TWW irrigation and to examine to what extent these effects are soil type dependent, we compiled a database with results from 24 peer-reviewed studies across different soil types containing information on the link between TWW irrigation, and hydraulic and physio-chemical properties through various measurements. The meta-analysis revealed that application of TWW significantly increases sodium adsorption ratio (on average 71 ± 6%) and electrical conductivity (on average 51 ± 5%) of soil as compared to the use of conventional water source. Overall, there were no significant effects on the soil pore space (bulk density, soil total porosity) or pH. Interestingly, the application of TWW significantly increased soil organic carbon and aggregate stability, potentially even benefiting soil structure. In addition, the organic compounds in TWW also might lead to hydrophobicity. Yet, the effects of TWW on soil hydraulic and physio-chemical properties are not consistent across different TWW types and soil classes. A larger number of studies is required to draw sound conclusions on this topic. Anyway, this analysis already indicated that different soil textures might react differently to TWW irrigation. While in medium-textured soils, salt accumulation was observed and TWW significantly increased soil organic carbon and saturated hydraulic conductivity, fine-textured soils are more prone to clogging and reduced in saturated hydraulic conductivity. We also noticed an impact of the type of TWW, since the degree of treatment has a big impact on the remaining components added to the soils together with the water. Primary TWW, from which settleable and floatable solids are removed, resulted in the highest accumulation of salts and significantly increased soil organic carbon and improved soil aggregate stability. However, the elevated biochemical oxygen demand or chemical oxygen demand in this type of TWW leads to an accumulation of organic materials in the soil, negatively affecting its permeability and reducing soil saturated hydraulic conductivity. This study stresses the need for more standardized experiments quantifying the effect of TWW not only in terms of transfer of contaminants and biosafety, but also an effect on soil quality, and more specifically soil physical quality, especially at the longer term.

The nutritional composition of six plant species after irrigation with treated wastewater and possible hazards by heavy metal accumulation.

A field experiment was conducted investigating the possibility of using treated wastewater (TWW) on sites affected by water scarcity in summer, waterlogging during the wet season, and salinity. A corresponding pot experiment was conducted comparable to the field experiment in Kalaât Landelous. The same plant species (Atriplex nummularia Lindl., Eucalyptus gomphocephala DC., Acacia cyanophylla Lindl., Casuarina glauca Sieber ex Spreng., Cupressus sempervirens L., and Pinus halepensis Mill.) were grown with the same treatments. While, in the field the plants, elemental composition cannot be linked to inputs by TWW, this was studied under controlled conditions. Additionally, a control was established lower in salinity receiving tap water. The effect of TWW irrigation on macro- and microelement uptake by the six plant species was studied. The treatments were high soil salinity under drained saline (DS) conditions, high salinity under waterlogged saline (WS), and a drained non-saline control (DNS: EC = 3.0 dS/m, pH = 8.4). TWW application under DS treatment increased Na, Cl, Ca, Mg, N, P, and K in most plant tissues compared to the control. TWW application in WS treatment resulted in an increase in heavy metals. Cu and Zn showed the highest bioaccumulation factor (BAF). The BAF in different plant tissues followed the order: Cu > Zn > Mn > Cd > Ni > Co > Pb. The plants accumulated significant amounts of metals in their roots.

Treated wastewater application in agriculture: potential assessment in the State of Santa Catarina/Brazil

This study aimed to evaluate the potential of using treated wastewater in the irrigation of 7 crops produced in the State of Santa Catarina by assessing the current demand for irrigation water in the study area and the future production of treated wastewater. Food production data were collected from the most significant public agricultural institution in the study area to calculate their blue water footprint, given the amount of food harvested. Future wastewater production data were gathered from official reports which present the sanitation plans to be performed by 2035. Geographic Information System tools and risk assessment approaches were used to present and discuss results from quantitative and qualitative perspectives. Results show that the amount of wastewater to be produced in 2035 could not only supply the current irrigation water demand for the selected crops but also allow agriculture to expand without consuming more potable water.

Assessment of three decades treated wastewater impact on soil quality in semi-arid agroecosystem

The use of treated wastewater (TWW) for crop irrigation is practiced in many countries worldwide as a strategy to offset water scarcity. Soil quality assessment is required to ensure that the application of this non-conventional irrigation water is sustainable over long periods. A relatively limited number of studies have used soil quality indexing approaches to investigate the impacts of TWW irrigation on soil quality. Therefore, this study aimed to assess the impacts of more than three decades of TWW irrigation on Fluvisol in semi-arid agrosystem to develop soil quality indices and evaluate their use as a practical tool to support TWW irrigation management. Overall, a total of 13 key soil attributes, used as soil quality indicators, were monitored in three TWW-irrigated plots and their adjacent non-irrigated control in eastern Tunisia. These selected indicators were used to develop a soil quality index (SQI) based on either a total data set (SQI-TDS) or a minimum data set (SQI-MDS) indexing approach. In comparison to the control, TWW application significantly increased saturated hydraulic conductivity (Ks) (+740%), saturation percentage (SP) (+20%), aggregate stability (AS) (+64%), field capacity (FC) (+52), electrical conductivity (EC) (+72%), phosphorous (P) (+472%), potassium (K) (+43%), organic matter (OM) (+90%) and basal respiration (BMR) (+117%) and decreased hydrophobicity (−17%), bulk density (BD) (−13%), cone penetration resistance (CPT) (−17%) and pH (−4%). The two developed SQI-TDS and SQI-MDS indices were sensitive to distinguish the impacts of TWW irrigation on soil quality in the study area. In comparison to the control, the TWW-irrigated soils exhibited higher SQI ratings by 42 and 52% based on SQI-MDS and SQI-TDS, respectively. Based on the monitored soil quality indicators in TWW-irrigated and control plots, this study indicates that long-term TWW application improved the overall soil quality and supports SQI-MDS’s efficiency in providing an adequate evaluation of soil quality in the study area.

Growth Development, Physiological Status and Water Footprint Assessment of Nursery Young Olive Trees (Olea europaea L. ‘Konservolea’) Irrigated with Urban Treated Wastewater

Application of urban treated wastewater (TWW) has been practiced globally as an alternative irrigation water source in areas where access to safe and abundant freshwater is limited. Water footprint (WF) has been employed over the last decades as a tool for the assessment of the sustainable management of water resources. In the present study, the suitability of TWW for the irrigation of nursery young olive trees (Olea europaea L. ‘Konservolea’), one of the main table olive cultivars in Greece, the second global table olive exporter, was tested and compared to tap water irrigation and application of zeolite on soil. Plant growth and physiological parameters and stress indicators were measured. Additionally, a WF assessment was performed, distinguishing TWW from freshwater (blue water) resources in order to examine the possibility of minimizing the environmental impact through the limitation of freshwater use. Plants irrigated with TWW performed better in most of the growth and physiological parameters measured compared to the other treatments. Stress indicators revealed that TWW did not induce any additional stress. TWW could be used as an irrigation water source for young olive trees for at least a short period during their growth as a safe and sustainable alternate of blue water resources. Additionally, the WF assessment showed that the application of TWW could be a significant blue water saving measure.

Treated wastewater irrigation effects on aggregate stability of Sandy loam soils in Semi-arid Tropical Zone of Nigeria

Irrigation with treated wastewater (TWW) for agricultural production is gradually becoming very important recycling option that substitutes fresh water (FW) particularly in water stressed regions like the Semi-arid Tropical zone of Nigeria. However, owing to high salt concentrations, dissolved organic matter and organic compounds found in the TWW occasionally, its application can have potential adversative impacts such as reduction of soil aggregate stability (SAS), which in turn affects soil quality. To assess the impact of TWW irrigation in comparison to FW irrigation on soils aggregation and SAS, wet sieving technique and the relationship of coefficient of variation (KV) and Mean Weight Diameter (MWD) were applied, while normal standard procedure was used for determination of some selected soil chemical and physical characteristics. The results indicated that the application of TWW increased the soil aggregate stability, and significantly highest (P<0.05) in phase III soils compared to other phases and control treated soils possibly due to relatively high organic matter content in the TWW sites compared to FW sites. Furthermore, the TWW is characterized by low concentration of salinity and sodicity parameters such as EC and Na, and comparatively high microbial glue like adhesive substances from the OC of the TWW soils. This in turn improve the aggregation, structural stability of the topsoil on one hand, and reduce the soils vulnerability to erosion on the other hand by binding micro-aggregates together to form macro-aggregates and larger pore spaces between micro-aggregates. Consequently, leading to improved water infiltration and permeability. Overall, the results indicated that the use of TWW for irrigation is a viable option, but care should be taken on the type and composition of the TWW particularly with regards to soluble salts concentration, organic and inorganic substances, as they can influence soils aggregate stability with other soil physical and chemical properties. This will consequently affect general soil quality and crop yield.

Impact of Wastewater Spreading on Properties of Tunisian Soil under Arid Climate

The environmental impacts of irrigating an olive field with olive mill wastewater (OMW) and treated wastewater (TWW) on soil properties were investigated. The effect of different irrigation treatments of OMW (50 m3 ha−1, 100 m3 ha−1, and 200 m3 ha−1) and TWW at different soil depths was studied. The obtained findings revealed that TWW application augmented soil pH; EC values; and P, K and Ca contents in all soil layers. However, Mg and Na concentrations, as well as organic matter content (OM), were proven to decrease with TWW irrigation throughout the experiment. Whereas soil adjusted with OMW showed a decrease in K, Ca, Mg and Na contents with soil depth, a significant increase was observed with the increase in applied OMW dose. On the other hand, total phenols and OM content increased significantly with the rise in OMW levels in all the investigated layers compared to the control sample.

Assessment of growth and yield of okra (Abelmoschus esculentus) under surface and subsurface drip irrigation using treated waste water

Purpose Due to increasing water demand in worldwide, treated wastewater (TWW) will become an important component in agriculture, particularly in countries facing the water scarcity. Using judiciously the already existing water resources in agriculture production can be proved by using efficient irrigation method. MethodsThis study investigates the impact of two irrigation water quality including; treated wastewater (TWW) and tap water (FW) with two modes of drip irrigation; subsurface at different depth (5, 15 and 25 cm depth) and surface drip irrigation on yield production and growth parameters of okra during the 2017 and 2018 growing seasons. Okra was chosen for its economical and nutritional values. Results Results revealed that the maximum agronomic performance of okra was recorded with TWW by comparing it with FW. SDI also offers more reliable growth and yield data than surface irrigation. TWW influenced positively the growth parameters and yield attitudes of okra. Plant height was maximum in WSDI25 treatment with 257 cm and 214 cm, in 2017 and 2018, respectively followed by WSDI15 and WSDI5 then WSDI0. The same order was observed for the different treatments in the plot by irrigated by FW. Fruit number per plant was observed to be maximum in WSDI5 (55.8) and WSDI15 (54.8), and minimum in FSDI0 (33.8) and FSDI5 (33.7). Okra yield was maximum in WSDI5 treatment (4.59 t/ha) and minimum in FSDI0 treatment (2.2 t/ha) in 2017. Conclusion The results of this study showed that application of TWW under (5 -15) cm depth of drip line is recommended for higher productivity of okra.

Utilização de água residuária tratada na recuperação da fertilidade de solo degradado no semiárido paraibano

<p class="Normal1"><span>O objetivo deste estudo foi avaliar o efeito da aplicação de água residuária tratada na recuperação dos teores de matéria orgânica e fósforo em um solo degradado na região semiárida. Foi realizado um experimento com irrigação de cinco espécies florestais da caatinga, no qual foram aplicados três tratamentos que consistiram na variação do tipo e do volume de água aplicados ao solo: 7 L por semana de água de abastecimento; 7 L por semana de água residuária; e 14 L por semana de água residuária. Após decorridos dois anos de irrigação, foram retiradas amostras do solo e analisadas quanto aos teores de matéria orgânica e fósforo. O teor de matéria orgânica no tratamento com aplicação de 14 L de água residuária em relação à aplicação de água de abastecimento foi cinco vezes superior na camada superficial e oito vezes na subsuperficial, respectivamente. A partir dos resultados encontrados, pode-se considerar que a utilização de água residuária de esgotos domésticos tratados é uma alternativa para a recuperação da capacidade produtiva do solo, pelo incremento nos teores de matéria orgânica e fósforo. A irrigação com água residuária tratada pode proporcionar incremento elevado nos teores de matéria orgânica e fósforo no solo até os 30 cm de profundidade.</span></p>

Treated Wastewater and Fertigation Applied for Greenhouse Tomato Cultivation Grown in Municipal Solid Waste Compost and Soil Mixtures

Low-fertility soil and the use of brackish water for irrigation act as obstacles and limit crop production. The utilization of municipal solid waste (MSW), compost (C), and treated wastewater (TWW) is receiving attention nowadays not only to overcome the above limitations but also as an efficient way for waste management and reuse of raw materials. In the present study, MSW compost in different ratios (5%, 10%, 20%, and 40%), fertigation and/or irrigation with TWW were studied in tomato plants (Solanum lycopersicum L.). The addition of compost increased organic content, pH, electrical conductivity (EC), and mineral content of the growing media, while fertigation and TWW supported the mineral status of the growing media, and this was reflected in the increase of N, K, and Na in tomato leaves. Plants grown in compost-based media with fertigation produced more leaves, compared to the control, while irrigation with TWW did not increase the number of leaves. Plant biomass increased with the application of ≥20% C, fertigation, and/or TWW applications. Plant yield increased in 40% C, while fertigation increased yield in case of lower (5%-10% C) compost ratios, but TWW application did not change the yield. The combination of high C ratios and fertigation and/or TWW decreased tomato fresh weight. Different levels of C did not affect leaf photosynthesis, stomatal conductance, internal CO2 concentration, and chlorophyll fluorescence, but, in general, the combination of compost with fertigation and/or TWW affected them negatively. Fruit total soluble solids, acidity, ascorbic acid, firmness, and total phenolics were increased with the high ratios of compost and/or fertigation and TWW applications, but marketability did not. Bacteria (total coliform and Escherichia coli) units increased in growing media subjected to TWW, but lower levels were counted on the fruit, mainly due to splashing or fruit contact with the soil. The results indicate that up to 40% C can be added into the substrate, as increased plant growth and maintained plant yield for greenhouse tomato cultivation is observed, while fertigation and TWW could be used in a controlled manner as alternative means for nutrient and irrigation in vegetables following safety aspects.

Mitigating negative effects of long-term treated wastewater application via soil and irrigation manipulations: Sap flow and water relations of avocado trees (Persea americana Mill.)

Recent studies have shown significant negative effects of long-term irrigation with treated wastewater (TWW) on performance of orchards planted on clay soil. The aim of this study was to evaluate water use and water relations of different mitigation measures to remedy the declining performance of a mature commercial fruit-bearing 'Hass' avocado orchard (Persea americana Mill.) growing in a clay soil irrigated with TWW since 2009. The mitigation measures, each in 6 replicates, included freshwater (FW), blended TWW:FW in a 1:1 ratio (MIX), low-frequency TWW irrigation (LFI), TWW irrigated tuff trenches (TUF) and TWW as the control treatment. The Penman-Monteith equation was used to determine reference evapotranspiration (mm day−1) and canopy conductance (mm s−1). A variety of climatic variables and tree physiological responses were monitored on continuous and seasonal bases. Measurements included sap flow (mm day−1), carbon isotope discrimination (δ13C), and trunk growth (cm). Whole plant hydraulic conductance (mm s−1 MPa−1) was estimated using the water potential gradient and sap flow. In summer when water use was highest sap flow values measured in 10 trees per treatment in FW, TUF and MIX were higher than TWW by up to 31 %, 26 %, and 24 %, respectively (p < 0.05). Treatment ranking based on sap flow (F), canopy conductance (gc), and whole plant hydraulic conductance (Kp) was FW> TUF > MIX > LFI > TWW. δ13C rankings were the same from low to high values, but with MIX > TUF. Most of the physiological parameters determined using different techniques have synergistically shown that using tuff trenches and mixing poor quality water (TWW) with fresh water are promising mitigating measures. Monitoring and evaluation should continue to determine if the alternatives contribute to sustainable yield increases in orchards on long-term bases.

Evaluation of selected plant species under drained saline and waterlogged conditions in pots when irrigated with treated wastewater

AbstractA pot experiment was carried out to study the effect of the use of treated wastewater (TWW) on selected plant species. In total three treatments were compared including high soil salinity under drained and waterlogging conditions in comparison to a drained non‐saline treatment. The effect of TWW on growth performance of the plant species was investigated to find out which of the plant species is most promising to be grown under the saline or waterlogged conditions when irrigated with TWW. The TWW application reduced the soil salinity even under the waterlogged conditions but more efficiently in drained soils. From the six plant species Atriplex nummularia, Acacia cyanophyllia and Eucalyptus gomphocephala performed better, with lower mortality and higher biomass production than Casuarina glauca, Cupressus sempervirens and Pinus halepensis. Salinity under the drained conditions in combination with TWW application even caused higher yields in case of Atriplex nummularia and Acacia cyanophyllia compared to a non‐saline soil.

Effects of Treated Wastewater on Soil Recovery in Degraded Semiarid Region

This study aimed to evaluate the effect of treated wastewater application on soil organic matter and phosphorus recovery in a degraded soil in the semiarid region of Brazil. An experiment was carried out with irrigation of five caatinga forest species, in which three treatments were applied that consisted in the variation of the type and volume of water applied to the soil, being 7 L per week of tap water, 7 and 14 L per week of wastewater. After two years of irrigation, soil samples were taken and analyzed for soil organic matter and phosphorus. The organic matter content in the treatment with 14 L application of wastewater was five times higher than application of tap water in the superficial layer and 8 times higher in the sub-surface, respectively. From the results obtained, it can be considered that the use of wastewater from treated domestic sewage serve as an alternative for the recovery of the productive capacity of the soil by the increase in the organic matter and soil phosphorus contents. Irrigation with treated wastewater can provide a high increase in soil organic matter and phosphorus content up to 30 cm deep.

Importance of soil texture to the fate of pathogens introduced by irrigation with treated wastewater

World-wide water scarcity is urging the use of treated wastewater (TWW) for irrigation but this practice may have adverse effects on soil and crop contamination due to the introduction of potential microbial pathogens. The objective of this study was to evaluate the potential health risks caused by TWW irrigation of soils differing in their texture, i.e., soil particle fractions including sand, silt and clay. We predicted that the presence of fecal indicator bacteria (FIB) and pathogens would not be linked to TWW irrigation, yet their abundance would be favored by the smallest soil fraction (~2 nm, e.g., clay) as it provides the largest surface area. To test our hypotheses, culture dependent and independent techniques were used to monitor the presence, abundance and source of FIB and microbial pathogens (bacteria and protists) in water (TWW and potable water) and three irrigated soil types (clay, loam and loamy-sand) in a field study spanning two years. The results showed that FIB and pathogens' abundance were significantly different between water types, yet these differences did not carry to the irrigated soils. The abundance and presence of FIB and potential opportunistic or obligate human pathogens did not significantly differ (p > 0.05) between TWW and potable water irrigated soils. Moreover, the source of the FIB and potential pathogens could not be linked to irrigation with TWW. Yet, soil type significantly altered the potential pathogens' diversity (p < 0.05) and abundance (p < 0.05), and differences were affected by clay content, as predicted. The results gave no indication for potential adverse health effects associated with the application of TWW but demonstrated that clay has a particular stabilizing effect on the potential presence of microbial pathogens.

Dissipation of Micropollutants in a Rewetted Fen Peatland: A Field Study Using Treated Wastewater

In the present study, a mixture of treated wastewater and surface water was used to rewet a degraded fen peatland site during a three-year rewetting experiment. We studied the behavior and effects of micropollutants by means of hydrological, physico-chemical, microbiological and ecotoxicological monitoring. The highest concentrations of micropollutants in the treated wastewater were found for the pharmaceuticals carbamazepine and diclofenac, some metabolites, the sweetener acesulfame, tolyl- and benzotriazole and diatrizoate. In the underlying, shallow groundwater where treated wastewater application for rewetting had been expected to have the greatest impact due to seeping and evapotranspiration processes, only a sporadic occurrence of micropollutants was found. The influence of dilution by groundwater movements was examined by applying a geohydrological model. The sorption of micropollutants onto the peaty soil also played a role, as found for carbamazepine. Further processes such as photolysis, microbial decay under low redox conditions and plant uptake can be assumed to be relevant for the removal of many substances. Ecotoxicity tests with the soil before and after rewetting did not indicate any negative impact on the soil habitat quality by wastewater application, but clearly pointed at ecotoxicologically relevant geogenic arsenic concentrations at the study site. Although a positive effect on receiving surface water systems is expected if wastewater is applied on land instead of discharged to water bodies, the rewetted soil may turn into a sink for micropollutants in the long term. Hence, the findings of the present field study encourage further investigations in order to identify the governing processes in the elimination of micropollutants in rewetted peatlands flooded with treated wastewater.

Impacts of Long-Term Irrigation of Domestic Treated Wastewater on Soil Biogeochemistry and Bacterial Community Structure.

Freshwater scarcity and regulations on wastewater disposal have necessitated the reuse of treated wastewater (TWW) for soil irrigation, which has several environmental and economic benefits. However, TWW irrigation can cause nutrient loading to the receiving environments. We assessed bacterial community structure and associated biogeochemical changes in soil plots irrigated with nitrate-rich TWW (referred to as pivots) for periods ranging from 13 to 30 years. Soil cores (0 to 40 cm) were collected in summer and winter from five irrigated pivots and three adjacently located nonirrigated plots. Total bacterial and denitrifier gene abundances were estimated by quantitative PCR (qPCR), and community structure was assessed by 454 massively parallel tag sequencing (MPTS) of small-subunit (SSU) rRNA genes along with terminal restriction fragment length polymorphism (T-RFLP) analysis of nirK, nirS, and nosZ functional genes responsible for denitrification of the TWW-associated nitrate. Soil physicochemical analyses showed that, regardless of the seasons, pH and moisture contents (MC) were higher in the irrigated (IR) pivots than in the nonirrigated (NIR) plots; organic matter (OM) and microbial biomass carbon (MBC) were higher as a function of season but not of irrigation treatment. MPTS analysis showed that TWW loading resulted in the following: (i) an increase in the relative abundance of Proteobacteria, especially Betaproteobacteria and Gammaproteobacteria; (ii) a decrease in the relative abundance of Actinobacteria; (iii) shifts in the communities of acidobacterial groups, along with a shift in the nirK and nirS denitrifier guilds as shown by T-RFLP analysis. Additionally, bacterial biomass estimated by genus/group-specific real-time qPCR analyses revealed that higher numbers of total bacteria, Acidobacteria, Actinobacteria, Alphaproteobacteria, and the nirS denitrifier guilds were present in the IR pivots than in the NIR plots. Identification of the nirK-containing microbiota as a proxy for the denitrifier community indicated that bacteria belonged to alphaproteobacteria from the Rhizobiaceae family within the agroecosystem studied. Multivariate statistical analyses further confirmed some of the above soil physicochemical and bacterial community structure changes as a function of long-term TWW application within this agroecosystem.

Heavy metal accumulation in soils and grains, and health risks associated with use of treated municipal wastewater in subsurface drip irrigation.

Constant use of treated wastewater (TWW) for irrigation over prolonged periods may cause buildup of heavy metals up to toxic levels for plants and animals, and entails environmental hazards in different aspects. However, application of TWW on agricultural land might be an effective and sustainable strategy in arid and semi-arid countries where fresh water resources are under great pressure, as long as potential harmful effects on the environment including soil, plants, and fresh water resources, and health risks to humans are minimized. The aim of this study was to assess the effect of deep emitters on limiting potential heavy metal accumulation in soils and grains, and health risk under drip irrigation with treated municipal wastewater. A field experiment was conducted according to a split block design with two treatments (fresh and wastewater) and three sub-treatments (0, 15, and 30cm depth of emitters) in four replicates on a sandy loam Calcic Argigypsids, in Esfahan, Iran. The annual rainfall is about 123mm, mean annual ETo is 1457mm, and the elevation is 1590m above sea level. A two-crop rotation of wheat (Triticum spp.) and corn (Zea mays) was established on each plot with wheat growing from February to June and corn from July to September. Soil samples were collected before planting and after harvesting for each crop in each year. Edible grain samples of corn and wheat were collected at harvest. Elemental concentrations (Cu, Zn, Cd, Pb, Cr, Ni) in soil and grains were determined using an atomic absorption spectrophotometer. Results showed that the concentrations of heavy metals in the wastewater-irrigated soils were not significantly different (P > 0.05) compared with the freshwater-irrigated soils. No significant difference (P > 0.05) in heavy metal content in soil between different depths of emitters was found. A pollution load index (PLI) showed that there was no substantial buildup of heavy metals in the wastewater-irrigated soils compared to the freshwater-irrigated soils. Cu, Pb, and Zn concentrations in wheat and corn grains were within the permissible US Environmental Protection Agency (EPA) limits, but concentrations of Cd (in wheat and corn) and Cr (in corn) were above the safe limits of the EPA. In addition, concentrations of Ni in wheat and corn seeds were several folds higher than the EPA standards. A health risk index (HRI) which is usually adopted to assess the health risk to hazard materials in foods showed values higher than 1 for Cd, particularly for wheat grain (HRI >2.5). Results also showed that intake of Cu through consumption of edible wheat grains posed a relatively high potential health risk to children (HRI >1.4), whereas children might also be exposed to health risk from Cd and Cr from corn grains (HRI >1.4). Based on aforementioned results, it can be concluded that the emitter depth in drip irrigation does not play a significant role in the accumulation of heavy metals from TWW in our sandy loam soil. Although their accumulation in the soil was limited and similar to using freshwater, uptake of Cd and Cr by wheat and corn was relatively large and hence resulted in health risk. The results suggest that more attention should be directed towards cultivation of other crops with drip irrigation system for a safe and more productive use of wastewater for irrigation. Alternatively, methods that filter the wastewater before it enters the soil environment might be an option that needs further investigation.

Water Quality and Toxic Element Effects on Isohumic Soil Properties and Crops in Semi-arid Regions.

Treated wastewater (TWW) and freshwater used separately or within the same agricultural soil is a key element in soil parameter evolution, soil-plant pollution and crop yields. The long-term application of TWW increased CaCO3, P, N, K, TOC, metal contents, pH and salinity in isohumic soil in semi-arid and arid climates. Also, it was found that using freshwater after TWW within the same land leached soil compounds and pollutants. Consequently, a clear decline of salinity, pH, macronutrient and pollutant concentrations occured. Therefore, the economic profitability in topsoil decreased. TWW contributed to crop production increase, despite high fertilizer and metal concentrations in TWW and soil. Also, no toxic metal trace was detected in cultivated plants despite soil pollution. Occasional rainwater removed the stable part of fertilizers in topsoil and slightly improved plant development.

Combined land application of treated wastewater and biosolids enhances crop production and soil fertility

Land application of treated wastewater (TWW) and biosolids is considered a cost-effective reuse method and valuable source of organic matter and nutrients. However, it may pose an adverse impact on the environment and human health. The main objective of this study is to determine the ability of land application of TWW and biosolids to enhance crop production and soil fertility. The study compared the effect of biosolids, commercial fertilizer, and manure on forage crop production (Zea mays). The soil and applied materials were analyzed before the experiment for major characteristics. Application rates were determined and calculated based on the crop nitrogen requirement, which is approximately 135 kg ha−1. Applied materials were incorporated uniformly in the top soil. Drip irrigation system was installed and Z. mays were sowed, and the plants were irrigated weekly with TWW to reach field capacity water content. At harvest, the crop yield and yield components were determined. Soil and plant samples were taken at the end of the experiment. Soil samples were analyzed for physical, chemical, and microbiological parameters. Plant samples were analyzed for essential nutrients, heavy metals, and biological analysis. The results have shown that, compared with the control, the crop yield increased similarly with the application of biosolids, commercial fertilizer, or manure. The yield increase was attributed to the increase in both leaves number and plant height that were affected similarly as the yield did. Plant macronutrient and micronutrient concentrations were not significantly affected by the treatments. However, the plant uptake of macronutrients and micronutrients similarly increased with biosolids, commercial fertilizer, and manure. On the other hand, Cd and Pb levels were below the detection limits. The results of soil analysis indicated that soil pH, EC, and SAR were not significantly affected by the treatments. However, CEC and OM significantly increased in the top soil with the application of biosolids, commercial fertilizer, or manure. DTPA-extractable micronutrients were not affected by the treatments. Soil and plant microbiological analysis indicated that Salmonella spp., IPN, and total fecal coliform count were not affected by the treatments and all samples were tested negative for enteric viruses. It can be concluded from this study that combined land application of TWW and biosolids improves crop production and enhances soil fertility level without significant impact on the environment and human health.