In this study, the quality of collected rainwater at a downtown middle school rainwater harvesting system was evaluated by measuring physical, chemical, and microbiological parameters such as pH, dissolved oxygen (DO), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), NO3, PO4, total coliform (TC), Escherichia coli , and some metals (i.e. Al, Cr, Mn, Zn, Cu, As, Cd, and Pb) (2003 to 2011). The analysis shows that the collected water quality is poor, which presents health, considering the high levels of bacterial indicators detected in the harvested rainwater, i.e. turbidity (1.4 to 15.5 NTU) and E. coli (120 and 35 CFU/100 mL in 2007 to 210 and 60 CFU/100 mL in 2011). This study shows that deteriorating water quality was caused by system contamination due to the absence of maintenance. Based on this study, proper operation and maintenance are generally the simplest and most effective ways of maintaining water quality.
Poor water quality and water shortage are becoming the biggest problems in urban areas (Vialle et al. 2011; Angrill et al. 2012; Rahman et al. 2014). Urban development and industrialization deteriorate water quality and contribute to water shortage (Farreny 2011; Lee et al. 2012). Collected rainwater is safe for consumption if its quality is maintained. It seems to be attractive because collected rainwater is relatively free from contamination compared to other water (e.g. surface water and groundwater) (Liaw et al. 2008; Lee et al. 2012; Rahman et al. 2014). However, its quality can deteriorate during harvesting, storage, and reuse. Dust, leaves, fecal droppings from birds, animals, and insects and contaminated litter on the catchment area can all cause contamination, leading to potential health risks from the reuse of the collected water reuse with poor quality (Vazquez et al. 2003; Evans et al. 2006; Sazakli et al. 2007). Currently, collected rainwater is widely used for toilet flushing and gardening purposes in South Korea. It could be used for showering, laundry, and so on (Kim & Lee 2004; Han & Park 2009). For drinking water purposes, sources of contaminations should be taken into account (Sazakli et al. 2007). Many studies have dealt with collected rainwater quality and have drawn contradictory conclusions (Simmons et al. 2001; Chang et al. 2004; Zhu et al. 2004; Lee et al. 2010; Abbasi & Abbasi 2011; Kwaadsteniet et al. 2013). The condition of the catchment influences the quality of the collected rainwater. Runoff from the catchment surface includes nonpoint pollutants (Kwaadsteniet et al. 2013) and contamination from corrugated roofing materials (e.g. heavy metals, paints, and coatings). Thus, maintenance must be performed for the removal of dirt, leaves, and other accumulated materials. Such cleaning should take place periodically before the start of rainfall. Conveyance systems are required to transfer the collected rainwater to its final point of use via collection devices (e.g. gutters and storage tanks). Corrosive metals may be transferred to the collected rainwater from metal roofs and pipes. Conveyance systems need to be periodically inspected and carefully cleaned to avoid contamination. Storage tanks should be carefully designed so that they offer drinking water with very low health risks. A poorly designed tank can pose high health risks from microbiological contamination. Storage tanks should be checked and cleaned periodically. Inappropriately high temperatures and external pollutants can cause microbial contamination. A secure cover is necessary to prevent mosquitoes from breeding and rodents from drowning. In the case of a rooftop and storage tanks, sunlight can penetrate the tank and cause algae to grow inside. The objective of this study is to show that maintenance may be one of the most important factors to ensure good water quality from rainwater harvesting systems.
MATERIALS AND METHODS
From 2002 to 2004, the system underwent regular maintenance and was kept secure according to a rainwater harvesting manual. The system was checked for rusting or leaking in gutters or pipes. The managers frequently checked that the gutter screens were not damaged or clogged with leaves or dirt. Also, they cleaned the catchment before rainfall events. The first flush device was cleaned out using drained water from the pipes after each rainfall event. Regularly, the rainwater tank was cleaned and disinfected to prevent slime, algae, bacterial growth and the build-up of sediments.
Sample collection and analysis
In this study, rainwater was collected from two tanks. The samples were collected in 1-L sterilized bottles from 2003 to 2011. The samples were then analyzed at a laboratory. Table 1 shows a summary of the analytical parameters and equipment (APHA 1995). Twenty five samples were analyzed in each year.
|.||Parameter .||Method and equipment .|
|Physical–chemical||pH, Turbidity||APHA (1995) & Thermo-orion 550A pH meter, HACH 2100P portable turbidimeter|
|COD, TSS, TN,PO4 TP||APHA (1995)|
|NO3, SO4||DIONEX ICS 3000|
|Metals||APHA (1995) & Perkin-Elmer ELAN 6100|
|Micro-biological||TC, E. coli||ISO method 9308-1|
Based on the analysis results for rainwater, descriptive statistics (box plot diagrams) were obtained using SPSS V.12 K software (SPSS Inc., USA). For correlation analysis, a nonparametric Spearman rank correlation analysis was performed to determine possible relationships among duration and physical-chemical and microbiological parameters.
RESULTS AND DISCUSSION
pH and turbidity
Chemical oxygen demand (COD)
Figure 2(c) shows a box plot diagram for variations in COD. In 2003, the research group did not perform measurements because the tank was found to be dirty. The average COD increased gradually by a factor of 9.2 from 2004 to 2011. The COD originated from nonpoint sources in the rooftop catchment and from biologic debris in the storage tank. The water quality rapidly deteriorated after 2009. This means that stored water could become contaminated and may contribute to the spread of pollutants (i.e. bacteria, organic matter, N and P) due to the absence of proper maintenance.
Total nitrogen (TN) and NO3
Total phosphorus (TP) and PO4
Figure 3(b) shows the average TP and PO4 concentrations that were monitored in 2004 to be 0.01 mg/L and 0 mg/L, respectively. TP and PO4 concentrations increased sharply owing to the cessation of maintenance in 2005. Although the Korean wastewater reclamation and reuse standard (KEOM 2013) amounts for TP and for PO4 are 0.2 mg/L and 0.01 mg/L respectively, the PO4 concentration in harvested rainwater exceeded the baseline 0.01 mg/L after 2005. The changes in TP and PO4 were similar to those of TN and NO3. However, the influence of TP and PO4 on contamination is minimal when compared to TN and NO3.
Al, Cr, Zn, Cu, Mn, As, Cd, and Pb
Figure 4 shows also the average Al concentration. Immediately after installing the rainwater utilization facility, the Al concentration ranged widely (20–190 μg/L) (not shown in this paper) because of Al dissolved from the concrete catchment. The average Al concentration of 63.0 μg/L is extremely low compared to the 200 μg/L limit set by the Korean drinking water standards (KEOM 2013).
Figure 4 shows that the average Zn concentration increased over time. Zn could originate from tank material. In general, the corrugated steel was coated with Zn to prevent corrosion caused by the harvested rainwater. Increasing Zn concentrations could be caused by tank corrosion. In 2011, the average Zn concentration was 517.0 μg/L, which is lower than the 1,000 μg/L limit set by the Korean drinking water standard.
Cu, Pb, Cr, Mn, As, Cd
The average Cu concentration increased sharply over time. Cu could originate from concrete materials and the facility system. However, it is at an extremely low concentration compared with the 1,000 μg/L limit set by the Korean drinking water standard. The average Pb concentration increased slightly over time from 22.8 to 35.9 μg/L. These metals originated from the catchment and storage tank. However, Cr, As, and Cd average concentrations were low compared with the 50 μg/L limit (Cr and As) and 10 μg/L limit (Cd) set by the Korean drinking water standards.
Total coliform (TC) and
Escherichia coli (EC)
Our statistical results suggest that harvested rainwater quality was dependent on both the duration over which the system was left without maintenance and the chemical-microbiological parameters shown in Table 2. Table 2 shows the correlation analysis that we carried out to derive relationships. Duration is significantly related to TC and EC activity, which is taken into account in our Spearman coefficient (ρ = 0.929 for TC and 0.881 for EC). This means that absence of maintenance is significantly related to the increases in TC and EC. In addition, Table 2 shows duration to be strongly related to COD (ρ = 0.99), TN (ρ = 0.98), NO3 (ρ = 0.98), TP (ρ = 0.98), and PO4 (ρ = 0.85). This study confirms that deterioration in water quality was caused by system contamination due to dry deposition from the atmosphere and animal activity exacerbated by the absence of maintenance.
|.||Turbidity .||CODcr .||TN .||NO3 .||TP .||PO4 .||TC .||EC .||Duration .|
|.||Turbidity .||CODcr .||TN .||NO3 .||TP .||PO4 .||TC .||EC .||Duration .|
The collected rainwater quality at a downtown middle school was evaluated by measuring physical, chemical, and microbiological parameters. The quality of the collected rainwater definitely depended on maintenance in rainwater harvesting systems. This study can be summarized as follows.
(1) Poor harvested rainwater quality indicates the need for improved education on the importance of maintenance in rainwater harvesting systems. Cleaning and hygiene maintenance is a good approach to minimize contamination.
(2) Possible contamination (i.e. metals and nutrients) in stored rainwater can be caused by the poor condition of parts of the rainwater harvesting system including the catchment, pipes and tanks.
(3) Maintenance and operation has a discernible impact on the quality of harvested rainwater for users
(4) Operators should follow a year-round checklist for potable or non-potable rainwater harvesting systems, including the following tasks:
Check tank water quality every month
Thoroughly clean the dripper and assembly parts every season
Check the screen and overflow pipe every month
Check particle filters every month
Disinfect the stored rainwater every month
Check the debris removal device every month
Check the cleaning tank every season
Clean the catchment every month.
This research was funded by Korea Environmental Industry & Technology Institute (KEITI), Seoul National University. The authors would like to thank members of the Rainwater Harvesting Center for their help and involvement in the completion of the project.