Pollutants in rainwater runoff in Korea: their impacts on rainwater utilization

Advancing rainwater treatment technologies for irrigation of urban agriculture: A pathway toward innovation

Urban agriculture (UA) has emerged for local food security since the 1960s. However, the access to sufficient and safe irrigation water remains a significant constraint. Municipal water supply, though commonly used in UA practices, proves unsustainable due to high costs, intensive energy consumption, and limited availability in many vacant urban spaces. In contrast, rainwater harvesting (RWH) exhibits a potential as a non-traditional water supply for urban farming. This article aims to provide insights into the advantages and challenges associated with RWH for UA irrigation, analyze existing low-cost RWH treatment technologies, and identify a visionary way toward innovative, new-generation RWH treatment processes in UA practices. Despite a promising water source, harvested rainwater is challenged for crop irrigation owing to the presence of various contaminants (e.g., waterborne pathogens, potentially toxic metals and metalloids, and synthetic organic chemicals). While established RWH treatment processes (e.g., first flush diversion, sedimentation, solar disinfection, chlorination, UV irradiation, granular filtration, and bio-sand filtration) can remove certain pollutants, they cannot offer viable treatment solutions for UA irrigation due to different technical, economic, and social restrictions. Particularly, their capacity to reliably remove contaminants of emerging concern in runoff remains limited or uncertain. Consequently, it is essential to develop next-generation RWH treatment technologies tailored specifically for UA irrigation. To this end, three fundamental principles are recommended. First, the focus should be on technically viable, low-cost, simple-operation, and easy-maintenance treatment technologies capable of simultaneously addressing traditional and emerging runoff contaminants, while minimizing the production of undesirable treatment byproducts. Second, advancing the understanding of the water, soil, and crop interactions enables the development of "right" RWH treatment processes for irrigation of "right" crops at a "right" place. Last, crop nutrients, if possible, are retained in rainwater to reduce the nutrient demand for crop production. The insights and perspectives have far-reaching implications for water conservation, stormwater management, and the integration of water, food, and energy systems within the urban environment.

The Life cycle Assessment Integrated with the Lexicographic Method for the Multi-Objective Optimization of Community-Based Rainwater Utilization

Community-based rainwater utilization (CB-RWU) has the advantage of easy maintenance and multiple benefits. However, its promotion proves to be a complicated task due to difficulties in quantifying and evaluating external benefits. This study integrated the life cycle assessment (LCA) with a multi-objective optimization model to optimize the relationship among all stages of CB-RWU, considering the trade-offs among the benefit-cost ratio, water-saving efficiency and environmental impact. The LCA results identified abiotic depletion potential for fossil fuels (ADPF) as the key impact indicators throughout the life cycle of CB-RWU. The optimal solution from the lexicographic method was 0.3098, 28.47% and 24.68 MJ for the benefit-cost ratio, water-saving efficiency and ADPF, respectively. Compared with the traditional optimization method, the lexicographic method improved the three object functions by 26%, 43% and 14%, respectively. The uncertainty of the environmental impact was the highest (C_V = 0.633) with variations in the floor area ratio, total runoff coefficient and reservoir volume. Changes in the total runoff coefficient were the main source of the uncertainty, which suggested that more attention should be paid to the area ratio of each underlying surface. In addition, economic support from the government is urgently required for the further promotion and development of CB-RWU.

Diversity and determinants of traditional water conservation technologies in the Eastern Cape Province, South Africa

Water scarcity remains a major threat to most rural areas in Africa due to heavy reliance on rainfed agriculture. This prompts the need to document and understand the determinants of traditional knowledge of water conservation practices. Our aim here is to document and identify the determinants of people's knowledge of traditional knowledge of water conservation in the South Africa's Eastern Cape province. A mixed research method was used. Purposive approach was used to collect data, i.e., elderly people were targeted during the face-to-face pre-COVID-19 pandemic interviews on the basis that traditional knowledge increases with age. However, people of different age groups were also included in the study especially when we employed only online questionnaire during the pandemic. We used questionnaire to collect all the data, and 93 people responded in total to our questions. We documented 10 traditional water conservation technologies. We identified rainfall variation, water quality issues, and increased water demand as the major challenges linked to these technologies, while easy access and the amount of water harvested are reported as benefits of these technologies. We found that traditional knowledge is not influenced by age (β =  -0.006 ± 0.01, P = 0.64) or gender (β =  -0.16 ± 0.25, P = 0.64) but rather correlates positively with geographic location, irrespective of the starting point of the distance measurement (distance from Port Elizabeth city: β = 0.002 ± 0.0008, P = 0.004; distance from Ngqushwa village: β = 0.0024 ± 0.0009, P = 0.008). Counterintuitively, formally educated people tend to have more traditional knowledge, but this is likely linked to the modern technologies (online survey and social media platforms) used to collect data during the COVID-19 pandemic. We suggest that traditional knowledge that has sustained life for centuries in rural communities must be integrated into water resource management to address water scarcity issues in rural Africa.

Road-deposited sediments mediating the transfer of anthropogenic organic matter to stormwater runoff

It has been regarded that road-deposited sediment (RDS) is one of the important sinks of anthropogenic pollutants as well as the major source of pollutants in stormwater runoff. However, the role of RDS, as a mediator of pollutants to the stormwater runoff, has not yet been investigated so far. Therefore, in this study, the leaching of dissolved pollutants, especially dissolved organic matter (DOM) from RDS, in synthetic precipitation was investigated. A significant amount of metals, nutrients, dissolved compounds, and DOM was leached. The leaching of DOM during 10 sequential leachings was 1811.3 and 2301.7 mg C/kg for larger (63 μm-2 mm) and smaller (< 63 μm) RDS, respectively. The results of UV/Vis spectroscopy, fluorescence spectroscopy, and size exclusion chromatography showed that the leached DOM was of anthropogenic/abiotic origins with lower molecular weight and humification degree. It is ubiquitous in stormwater runoff and industrial discharges and differs from natural organic matter. The results strongly suggest that RDS is an important mediator transferring anthropogenic pollutants to stormwater runoff. In addition, the removal of RDS, such as sweeping, would significantly reduce the pollutants input to the runoff.

Oxidative Treatments of Pesticides in Rainwater Runoff by HOCl, O3, and O3/H2O2: Effects of pH, Humic Acids and Inorganic Matters

This study systematically investigated the oxidative treatment of five selected pesticides, alachlor (ALA), carbendazim (CAR), diuron (DIU), pyrimethanil (PYR), and tebuconazole (TEB), by comparing their relative reactivities as a function of three different oxidative treatment processes (i.e., chlorine (HOCl), ozone (O3), and ozone/hydrogen peroxide (O3/H2O2)) under various oxidant dosages, reaction times, and pH conditions. For oxidative treatment, pesticide standards were spiked into rainwater. The removal efficiency of the selected pesticides varied considerably depending on the oxidative treatment processes. HOCl, O3, and O3/H2O2 treatments were highly effective at eliminating CAR (>80%) and PYR (>99%), while they were not significantly effective in removing TEB (<20%). In the case of DIU, HOCl (81%) was shown to be more effective than O3 (24%) and O3/H2O2 (49%). The removal efficiency of ALA was in the order of O3/H2O2 (49%) > O3 (20%) > HOCl (8.5%). The effect of increasing the solution pH from 5.0 to 9.0 on pesticide degradation varied between the oxidative treatment processes. Additionally, NH4+, NO2−, and humic acid in rainwater significantly inhibited pesticide degradation.

Mitigation Plan and Water Harvesting of Flashflood in Arid Rural Communities Using Modelling Approach: A Case Study in Afouna Village, Egypt

This paper aims to propose methods to mitigate the risks of flash flood events in arid rural communities with poor infrastructure. A flash flood management case study was conducted at Afouna Village in Egypt, which is characterized by an arid climate and faced a devasting flash flood in 2015. First, the flash flood was modelled and it was found that it corresponds to a 100 year return period flood that led to an almost 13 million m3 total runoff volume. A structural protection approach, using an artificial infiltration pond, was applied to mitigate the flooding risks through water harvesting and recharging the groundwater of the Moghra aquifer. In this study, a novel approach was proposed, which is substituting the low permeability silty sand (2.0 × 10−4 m/s) in the pond area with a high permeability one (9.6 × 10−3 m/s), which will enhance water harvesting and reduce direct evaporation. Modern techniques of hydrological modelling were utilized in order to achieve the optimal use, and harvesting, of flash flood water.

Evaluation of effect of hazardous contaminants in areas for the abstraction of drinking water

The lower portion of Taquari River is influenced by compounds from anthropic activities causing concern about the drinking water supplied to cities in the region. The study objective was to investigate the presence of contaminants at drinking water abstraction sites, defining the mutagenic effects of these stressors as an ecosystem quality parameter and its possible effects on human health. Geographic Information System techniques were used to investigate sources of contamination and it was found that agricultural activities predominated with a few medium and high potential pollutant agricultural activities, besides a soil area that was contaminated and undergoing an intervention process. Mutagenic effects were evaluated by Salmonella/microsome assay using TA98, TA97a, TA100, YG1041 and YG1042 strains in the presence and absence of metabolic activation (S9). Mutagenesis found in organic sediment extracts and surface water samples showed the prevalence of direct-acting mutagens at the drinking water abstraction sites. Taquari (Ta032, the sampling points were named according to the initial letters of the river (Ta), followed by the number of kilometers from the mouth) showed the highest mutagenic potency in sediment, while Ta063, at Bom Retiro do Sul, presented it in the water sample. In the Triunfo region (Ta011) there were significant responses in sediment and in water samples. The samples at General Câmara (Ta006) showed the least presence of contaminants. The Allium cepa test applied to sediments in natura showed significant micronucleus induction in Ta032 in accordance with the Salmonella/microssome assay. The test performed on Danio rerio embryos (FET) in the in natura water samples did not present significant responses. Chemical analyses of polycyclic aromatic hydrocarbons and metals already identified as chemical markers in the area indicated a small contribution to the mutagenic potency, calling attention to the fact that other direct-acting pollutants may be present at the drinking water abstraction sites.

Rainwater as a Source of Drinking Water: Health Impacts and Rainwater Treatment

Rainwater is the main source of drinking water in tropical communities, especially in West Kalimantan. Air contamination causes rainwater to become acidic and cloudy and adds heavy metals such as Pb into rainwater. In addition to pollution, the way in which the rainwater is collected such as through zinc roofing also exposes the rainwater to heavy metals. The presence of Pb in rainwater will have an impact on the health of the community in the long run. The model of simple water treatment using filtration is needed to overcome this problem with the use of media available in the region. The media used are in the form of mollusk sand and activated carbon. In the end, the mollusk sand filtration model and activated carbon sorption were effectively used to filter polluted rainwater to be safe for consumption.

Assessment of Rainwater Harvesting Systems in Poor Rural Communities: A Case Study from Yatta Area, Palestine

Yatta is a town located nine kilometers south of Hebron city in the West Bank of Palestine. The town houses over 100,000 people of which 49% are females and has a population that doubles every 15 years. Yatta has been connected to a water network since 1974 serving nearly 85% of its households. The water network is old and inadequate to meet the needs of the population. Water supply made available to the area is limited, estimated at 20 L/capita/day. Residents are thus forced to rely on water vendors who supply water that is 400% more expensive with a lower quality compared to municipal water. Therefore, rainwater harvesting is a common practice in the area, with the majority of households owning at least one cistern. Rainwater harvesting is of great socio-economic importance in areas where water sources are scarce and/or polluted. In this research, the quality of harvested rainwater used for drinking and domestic purposes in Yatta was assessed throughout one year. A total of 100 samples were collected from cisterns with an average capacity of 69 m3, which are adjacent to cement-roof catchment areas of 145 m2 average surface area. Samples were analyzed for a number of parameters including temperature, pH, alkalinity, hardness, turbidity, total dissolved solids, NO3, NH4, chloride and salinity. Results showed that most of the rainwater samples were within World Health Organization (WHO) and Environment Protection Agency (EPA) guidelines for chemical parameters. Microbiological contents such as total Coliforms and faecal Coliforms bacteria were tested. The research also addressed the impact of rainwater harvesting systems on different socio-economic attributes of the local community through a questionnaire that had been filled out before any sample was collected.

Improving stormwater quality at source using catch basin inserts

Stormwater runoff transports contaminants, including gross pollutants (GPs) accumulated on surfaces to nearby receiving water bodies. These may clog storm drainage systems, seal side entry pits and increase dissolved pollutants in receiving water bodies. Best management practices (BMPs) such as oil and grit separators, grassed swales, vegetated filter strips, retention ponds, and catch basin inserts (CBIs) are implemented to reduce stormwater pollutants in urban runoff. However, the information on physicochemical characteristics of the pollutants are still few in literature but important to improve the design of BMPs, considering qualitative aspects, and their operation. CBIs are devices used to remove GPs at source without requiring any extra land use because they are typically mounted within a catch basin (e.g. side entry pit) or existing drain. In this study, improvement of stormwater quality was investigated at two different sites (Subiaco, a residential area and Hillarys Boat Harbour, a commercial-marine-recreational area; Western Australia) where a new CBI made of non-woven polypropylene geotextile was installed in side entry pits to capture GPs at source. Influent and effluent water from the CBIs was collected and analyzed for BOD, COD, TSS and PO₄-P with maximum improvements in water quality of 90%, 88%, 88% and 26% respectively. The heavy metals in influent and effluent water were found very low and below the guideline values. Analysis of particle size distribution, specific surface area of solids, SEM images and heavy metal content (Cu, Fe, Ni, Pb, Zn, Cd) in solids showed that the residential area contained more finer particles than the commercial area but that solids in the commercial area contained greater concentrations of heavy metals than those from the residential area. The specific surface area was found to be higher in the residential area and particles were thought to be largely sourced from traffic. However, these characteristics may be monitored for longer term for more CBIs installed in different locations.

Sustainability of rainwater harvesting system in terms of water quality

Water is considered an everlasting free source that can be acquired naturally. Demand for processed supply water is growing higher due to an increasing population. Sustainable use of water could maintain a balance between its demand and supply. Rainwater harvesting (RWH) is the most traditional and sustainable method, which could be easily used for potable and nonpotable purposes both in residential and commercial buildings. This could reduce the pressure on processed supply water which enhances the green living. This paper ensures the sustainability of this system through assessing several water-quality parameters of collected rainwater with respect to allowable limits. A number of parameters were included in the analysis: pH, fecal coliform, total coliform, total dissolved solids, turbidity, NH3-N, lead, BOD5, and so forth. The study reveals that the overall quality of water is quite satisfactory as per Bangladesh standards. RWH system offers sufficient amount of water and energy savings through lower consumption. Moreover, considering the cost for installation and maintenance expenses, the system is effective and economical.

A review of ion and metal pollutants in urban green water infrastructures

In urban environments, the breakdown of chemicals and pollutants, especially ions and metal compounds, can be favoured by green water infrastructures (GWIs). The overall aim of this review is to set the basis to model GWIs using deterministic approaches in contrast to empirical ones. If a better picture of chemicals and pollutant input and an improved understanding of hydrological and biogeochemical processes affecting these pollutants were known, GWIs could be designed to efficiently retain these pollutants for site-specific meteorological patterns and pollutant load. To this end, we surveyed the existing literature to retrieve a comprehensive dataset of anions and cations, and alkaline and transition metal pollutants incoming to urban environments. Based on this survey, we assessed the pollution load and ecological risk indexes for metals. The existing literature was then surveyed to review the metal retention efficiency of GWIs, and possible biogeochemical processes related to inorganic metal compounds were proposed that could be integrated in biogeochemical models of GWIs.

Roof selection for rainwater harvesting: quantity and quality assessments in Spain

Roofs are the first candidates for rainwater harvesting in urban areas. This research integrates quantitative and qualitative data of rooftop stormwater runoff in an urban Mediterranean-weather environment. The objective of this paper is to provide criteria for the roof selection in order to maximise the availability and quality of rainwater. Four roofs have been selected and monitored over a period of 2 years (2008-2010): three sloping roofs - clay tiles, metal sheet and polycarbonate plastic - and one flat gravel roof. The authors offer a model for the estimation of the runoff volume and the initial abstraction of each roof, and assess the physicochemical contamination of roof runoff. Great differences in the runoff coefficient (RC) are observed, depending mostly on the slope and the roughness of the roof. Thus, sloping smooth roofs (RC>0.90) may harvest up to about 50% more rainwater than flat rough roofs (RC=0.62). Physicochemical runoff quality appears to be generally better than the average quality found in the literature review (conductivity: 85.0 ± 10.0 μS/cm, total suspended solids: 5.98 ± 0.95 mg/L, total organic carbon: 11.6 ± 1.7 mg/L, pH: 7.59 ± 0.07 upH). However, statistically significant differences are found between sloping and flat rough roofs for some parameters (conductivity, total organic carbon, total carbonates system and ammonium), with the former presenting better quality in all parameters (except for ammonium). The results have an important significance for local governments and urban planners in the (re)design of buildings and cities from the perspective of sustainable rainwater management. The inclusion of criteria related to the roof's slope and roughness in city planning may be useful to promote rainwater as an alternative water supply while preventing flooding and water scarcity.

Rainwater utilization and storm pollution control based on urban runoff characterization

The characteristics of urban runoffs and their impact on rainwater utilization and storm pollution control were investigated in three different functional areas of Zhengzhou City, China. The results showed that in the same rain event the pollutant loads (chemical oxygen demand (COD) and total suspended solids (TSS)) in the sampling areas were in the order of industrial area > commercial area > residential area, and within the same area the COD and TSS concentrations of road runoffs were higher than those of roof runoffs. The first flush effects in roof and road runoffs were observed, hence the initial rainwater should be treated separately to reduce rainwater utilization cost and control storm pollution. The initial roof rainfall of 2 mm in residential area, 5 mm in commercial area and 10 mm in industrial area, and the initial road rainfall of 4 mm in residential area and all the road rainfall in commercial and industrial areas should be collected and treated accordingly before direct discharge or utilization. Based on the strong correlation between COD and TSS (R2, 0.87-0.95) and the low biodegradation capacity (biochemical oxygen demand BOD5/COD < 0.3), a sedimentation process and an effective filtration system composed of soil and slag were designed to treat the initial rainwater, which could remove over 90% of the pollutant loads. The above results may help to develop better rainwater utilization and pollution control strategies for cities with water shortages.

Rooftop runoff as a source of contamination: a review

Scientific reports concerning chemical and microbiological contaminant levels of rainwater runoff from rooftop collection in both urban and rural areas are reviewed. This alternative source of water has been documented to often contain substantial amounts of contaminants. Studies describing levels of heavy metal contamination specific to runoff from rooftop catchment areas containing exposed metal surfaces are discussed. Depending upon the intended use, scientific evidence is also accumulating that various treatments and disinfections will be required prior to release of roof-runoff water either into surface waters or for more direct consumer usage. For microbial contamination, current proposed standards and guidelines regarding this type of water source are shown to vary widely worldwide. Scientific literature reveals a lack of clarity regarding water quality guidelines and health related standards for certain types of rooftop runoff. Studies suggests that rainwater collection systems which are properly designed, maintained, and treated may provide a valuable supplement to existing water supplies by reducing demand on community water supplies/infrastructure costs, enhancing effective management of storm water runoff, and increasing restoration of underground reservoirs through controlled infiltration.

Changes in abundance of heterotrophic and coliform bacteria resident in stored water bodies in relation to incoming bacterial loads following rain events

Microbial properties of harvested rainwater were assessed at two study sites at Newcastle on the east coast of Australia. The investigation monitored daily counts of heterotrophic bacteria (HPC), total coliforms and E. coli during a mid-winter month (July). Immediately after a major rainfall event, increases in bacterial loads were observed at both sites, followed by gradual reductions in numbers to prior baseline levels within 7 days. Baseline HPC levels ranged from 500-1000 cfu/mL for the sites evaluated, and the loads following rain peaked at 3590-6690 cfu/mL. Baseline levels of total coliforms ranged from 0-100 cfu/100 mL and peaked at 480-1200 cfu/100 mL following rain. At Site 1, there was no evidence of E. coli loading associated with the rain events assessed, and Site 2 had no detectable E.coli colonies at baseline, with a peak load of 17 cfu/100 mL following rain which again diminished to baseline levels. It was concluded that rainfall events contributed to the bacterial load in rainwater storage systems, but processes within the rainwater storage ensured these incoming loads were not sustained.