Efficiency of a closed-coupled solar pasteurization system in treating roof harvested rainwater

Science of the Total Environment 536 (2015) 206–214

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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Efficiency of a closed-coupled solar pasteurization system in treating roof harvested rainwater P.H. Dobrowsky a, M. Carstens a,1, J. De Villiers b, T.E. Cloete a, W. Khan a,⁎ a b

Department of Microbiology, Faculty of Science, Stellenbosch University, Stellenbosch, South Africa Crest, Po Box 7129, Stellenbosch 7599, South Africa

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Solar pasteurization system used to produce large quantities of potable water. • Aluminum, lead and nickel leached from the stainless steel holding tank. • Indicator bacteria reduced to below the detection limit at temperatures above 72 °C. • Bacteria detected (PCR) in tank water samples pasteurized at 72 °C and above. • Viability of specific pathogenic bacteria needs to be determined.

a r t i c l e

i n f o

Article history: Received 13 March 2015 Received in revised form 22 June 2015 Accepted 28 June 2015 Available online xxxx Editor: Simon Pollard Keywords: Roof harvested rainwater Solar pasteurization Pathogens Chemical and microbial quality

a b s t r a c t Many studies have concluded that roof harvested rainwater is susceptible to chemical and microbial contamination. The aim of the study was thus to conduct a preliminary investigation into the efficiency of a closed-coupled solar pasteurization system in reducing the microbiological load in harvested rainwater and to determine the change in chemical components after pasteurization. The temperature of the pasteurized tank water samples collected ranged from 55 to 57 °C, 64 to 66 °C, 72 to 74 °C, 78 to 81 °C and 90 to 91 °C. Cations analyzed were within drinking water guidelines, with the exception of iron [195.59 μg/L (55 °C)–170.1 μg/L (91 °C)], aluminum [130.98 μg/L (78 °C)], lead [12.81 μg/L (55 °C)–13.2 μg/L (91 °C)] and nickel [46.43 μg/L (55 °C)–32.82 μg/L (78 °C)], which were detected at levels above the respective guidelines in the pasteurized tank water samples. Indicator bacteria including, heterotrophic bacteria, Escherichia coli and total coliforms were reduced to below the detection limit at pasteurization temperatures of 72 °C and above. However, with the use of molecular techniques Yersinia spp., Legionella spp. and Pseudomonas spp. were detected in tank water samples pasteurized at temperatures greater than 72 °C. The viability of the bacteria detected in this study at the higher temperature ranges should thus be assessed before pasteurized harvested rainwater is used as a potable water source. In addition, it is recommended that the storage tank of the pasteurization system be constructed from an alternative material, other than stainless steel, in order for a closed-coupled pasteurization system to be implemented and produce large quantities of potable water from roof harvested rainwater. © 2015 Elsevier B.V. All rights reserved.

⁎ Corresponding author. E-mail address: [email protected] (W. Khan). 1 M. Carstens has previously published under the name M. De Kwaadsteniet.

http://dx.doi.org/10.1016/j.scitotenv.2015.06.126 0048-9697/© 2015 Elsevier B.V. All rights reserved.

P.H. Dobrowsky et al. / Science of the Total Environment 536 (2015) 206–214

1. Introduction While many factors influence the quality of natural water resources, added pressures, including the growth of the worlds' population and climate change, have forced authorities around the world to find alternative water sources to meet the increasing demands for potable water (Ahmed et al., 2011). Roof harvested rainwater may serve as an alternative source of drinking water, but only if the water meets the international standards of drinking water as stipulated by the World Health Organization (WHO, 2011). Contamination of the rainwater may however, occur while the water traverses through the air, on contact with the roofing system (catchment area), drainage pipes and in the storage tank of the rainwater harvesting system (Abbasi and Abbasi, 2011). Numerous chemical and microbial pollutants have thus been detected in untreated rainwater sources (Spinks et al., 2006; Ahmed et al., 2008, 2010, 2012; Huston et al., 2012) and if the harvested rainwater is utilized as a primary potable water source, this could result in adverse health effects. The development of effective harvested rainwater treatment methods are thus required to provide a clean and safe drinking water source to the public and especially to rural communities and informal settlements in urban areas, who may utilize harvested rainwater as a primary water source. Solar pasteurization may be utilized as a possible treatment for contaminated water sources as microorganisms are susceptible to heat (pasteurization) and ultraviolet-A radiation. The sun is a free, natural source of energy and its full potential remains untapped. Solar pasteurization (SOPAS) differs from solar disinfection (SODIS) in that the SOPAS reactor inactivates microorganisms by using the thermal effect at a temperature of at least 70 °C without radiation, whereas the SODIS reactor uses both the thermal effect and UV-A radiation (Sommer et al., 1997). According to Nieuwoudt and Mathews (2005), the technology of heating water to below boiling temperature has gained much interest and for this reason the design and implementation of heat based disinfection systems is fairly advanced. Currently, there are three types of passive water heating systems that are manufactured predominantly for domestic use (Solar Energy Equipment, 2000; Nieuwoudt and Mathews, 2005; South African Bureau of Standards, SABS, 2012). The most expensive system is a split system manufactured from two components, namely, a collector and a storage tank, whereby water is heated directly or indirectly. An indirect heating system is defined by the SANS 1307 (South African Bureau of Standards, SABS, 2012) guidelines as a system “in which an absorber transfers heat via a heat exchanger to the potable water to be heated,” whereas in a direct heating system “the potable water to be heated is circulated through the absorber, and the solar heat gathered by the collector is transferred directly to the potable water itself.” The collector is usually installed on the northfacing area of the roof and the storage tank inside the roof. The second closed-coupled system is comprised of a flat plate collector, that can heat water directly or indirectly, and a separate elevated storage tank attached to the end of the collector. It has been noted that these systems are less expensive and installation is easier than the split systems. Lastly, a less efficient closed system, is the integrated collector storage, or the integral collector (ICS) system comprising of a collector that is used to heat and store the water. These systems are the most cost effective. Close-coupled systems are also usually placed on the north-facing section of pitched roofs (Nieuwoudt and Mathews, 2005). The aim of this study was to conduct a preliminary assessment of the efficiency of a closed-coupled solar pasteurization system, in treating harvested rainwater at different pasteurization temperatures. The microbial parameters that were investigated included the enumeration of total coliforms, Escherichia coli (E. coli) and heterotrophic bacteria. In addition, the treated and untreated tank water samples of the pilot scale study were screened for the presence of selected bacteria genera, considered ubiquitous in rainwater sources, using conventional polymerase chain reaction (PCR). The chemical parameters that were investigated during the pilot scale study included the concentration of metal ions, anions

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and cations present in the treated and untreated tank water samples. Readings for both solar radiation and the temperature of the tank water within the pasteurization system were recorded every 30 min. The volume of potable water that the system could produce at a given temperature was also determined. 2. Materials and methods 2.1. Sample site and collection A polyethylene rainwater harvesting (RWH) tank (2000 L) was installed at the Welgevallen experimental farm (33°56′36.19″S, 18°52′ 6.08″E), Stellenbosch University, South Africa. First flush diverters were not installed above the tanks, as certain studies have suggested that first flush diverters do not minimize the microbial contamination found in harvested rainwater. For example, Gikas and Tsihrintzis (2012) noted that the installation of a first flush rainwater diverter improved the physicochemical quality of the harvested rainwater, but did not improve the concentration of microbial pollutants. The sampling site was surrounded by trees; however, no tree branches obstructed the catchment area. The farm was also surrounded by dirt roads that were frequently used by motor vehicles and the farm workers to herd cattle twice a day, as the tanks were situated on the northern side of a wellestablished building that neighbored the farms' dairy. Samples were collected from July to October 2013 at various temperature ranges (55 to 57 °C; 64 to 66 °C; 72 to 74 °C; 78 to 81 °C; 90 to 91 °C). Three sampling events were performed for each temperature range, with a total of 15 sampling sessions conducted overall. For each temperature before (untreated) and 1 L of heat treated tank water was collected in duplicate. Microbial analysis was thus performed on 15 untreated tank water samples and 30 heat treated tank water samples, with 45 tank water samples analyzed in total. For the determination of the metal concentrations, Falcon™ 50 mL high-clarity polypropylene tubes containing polyethylene caps were pre-treated with 1% nitric acid before each sampling session. 2.2. Solar pasteurization system The Apollo™ solar pasteurization system was designed and manufactured in China and donated to Stellenbosch University by Crest, a company in Stellenbosch, South Africa. For ease of sampling, the rainwater tank was installed on a metal stand so that the rainwater could flow from the tank into the solar pasteurization system in a passive manner (Fig. 1). The water from the rainwater tank flowed through the systems' components as follows (Fig. 1); firstly, cold water flowed from the rainwater tank (A) through the cold water feed (B) into the cold water stainless steel inlet tank (D). To increase the flow rate into the inlet tank it is suggested that larger, shorter pipes with gentle bends be utilized in the system. From the inlet tank, cold water flowed into the stainless steel main storage tank (E) (capacity: 100 L) then down through the 12, 1.7 m × 0.047 m, high borosilicate glass evacuated tubes (F). The direct solar radiation heats the high borosilicate glass evacuated tubes (aperture area: 0.96 m2) which are lined with black paint in order to capture heat. Through the principle of thermo-siphoning, as the cold water (blue arrow) heats it loses density and becomes more buoyant. The heated water was then able to move up (red arrow) into the main storage tank (E). If the process of hot water being replaced by colder more dense water continues, the whole body of water in the main tank will heat up (Apollotechnology, 2013). Untreated tank water samples were collected from the rainwater tank (A) and pasteurized tank water samples were collected from the hot water outlet (G). A MadgeTech — Thermocouple Temperature Data Logger TC101A (Madge Tech, Inc) was installed to monitor the temperature of the harvested rainwater inside the storage tank of the solar pasteurization system. To ensure that only the less dense warm water was being monitored, the probe of the logger was passed through the inlet tank and

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The temperature and pH of the tank water collected at the sampling locations were measured using a hand-held mercury thermometer and color-fixed indicator sticks with a pH range of 0–14 (ALBET®, Barcelona, Spain). 2.4. Recovery of indicator organisms To enumerate heterotrophic bacteria, a serial dilution was prepared for each sample (10−1–10−2) and 100 μL of each dilution was inoculated onto R2A agar (Difco) by use of the spread plate method, with the plates incubated at 37 °C for up to 4 days. Total coliforms (TC) and E. coli were enumerated simultaneously by filtering a total volume of 100 mL (undiluted and 10−1) through a sterile GN-6 Metricel® S-Pack Membrane Disc Filter (Pall Life Sciences, Michigan, USA) with a pore size of 0.45 μm and a diameter of 47 mm. The filtration flow rate was approximately ≥65 mL/min/cm2 at 70 kPa. The filters were incubated on Membrane Lactose Glucuronide Agar (MLGA) (Oxoid, Hampshire, England) at 35 ± 2 °C for 18–24 h (U.S. Environmental Protection Agency, 2009). All analyses were performed in triplicate. 2.5. The bacterial removal efficiency of the pasteurization system and the quantity of pasteurized harvested tank water produced

Fig. 1. A low pressure solar pasteurization system (ASLP-12/1800-58) was utilized in the current study. The labels and corresponding components of the solar pasteurization system are indicated: A: Rainwater harvesting tank, B: Cold water feed into the inlet tank, C: Exhaust pipe, D: Cold water inlet tank, E: Main storage tank, F: 12 × Collector tubes, and G: Hot water outlet. A schematic diagram of the interior of the storage tank is represented by H whereby less dense heated water will rise and exit through the outlet.

The bacterial removal efficiency of the system was obtained by comparing the bacterial numbers obtained from the samples collected before pasteurization and the average bacterial numbers obtained from samples collected after pasteurization. The log reduction and the percentage reduction was calculated (Brözel and Cloete, 1991). Log reduction ¼ Log10 bacterial countbefore pasteurization – Log10 bacterial countafter pasteurization




ð1Þ approximately half way into the storage tank (indicated by a black arrow in Fig. 1). The temperature data obtained from the log tagger was analyzed using Data Logger Software version 4.1.5. Rainfall and temperature patterns were obtained from the South African Weather Services (Pretoria, South Africa), while direct solar radiation data was obtained from Stellenbosch Weather Services, Engineering Faculty, Stellenbosch University (http://weather.sun.ac.za/). In order to monitor the temperature fluctuations of the pasteurized tank water, the temperatures of the pasteurized roof harvested tank water samples as well as the ambient temperature were monitored for approximately one month (26.07.2013–24.08.2013). The direct solar radiation (W/m2) data was obtained for the same time period (26.07.2013–24.08.2013). Readings for both the solar radiation and the temperature were recorded every 30 min. 2.3. Chemical analysis Unpasteurized and pasteurized tank water samples collected for the various temperature ranges, namely, 55 °C, 65 °C, 78 °C and 91 °C, were analyzed for the presence of metals and cations including aluminum (Al), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu) and zinc (Zn), amongst others. Cations were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) according to Saleh et al. (2000) and nitric acid digestion. All samples were analyzed for the presence of metals at the Central Analytical Facility (CAF), Stellenbosch University. The unpasteurized and pasteurized tank water samples were also sent to the Centre for Scientific and Industrial Research (CSIR), Stellenbosch for anion analyses using SALM 7.0 Automated Colorimetry (nitrate and nitrite), SALM 9.0 Automated Colorimetry (soluble phosphate), MALS 6.5 ICP OES Detection (sulfate), SALM 1.0 Automated Colorimetry (chloride) and SALM 11 Potentiometric measurement (fluoride). All anion analyses were performed in accordance with the recognized International Standard ISO/IEC, 17025:2005.

Percentage reduction ¼ 100−ðSurvivor count=Initial countÞ  100

ð2Þ

For each temperature range, the volume of pasteurized tank water (m = kg/h) produced by the closed coupled system was calculated as previously described by Klein (1975). Whereby the useful heat gain (Q) is dependent on the mass flow rate (m), specific heat (cp) and a change in temperature from the inlet (Ti) to the outlet (To) of the storage tank. Q ¼ mcp ðT o –T i Þ

ð3Þ

m ¼ Q=cp ðT o –T i Þ

ð3bÞ

The volume of treated water produced by the solar pasteurization system was determined in order to ascertain whether an adequate potable water supply would be available for individual households. 2.6. Extraction of total DNA from tank water samples Total DNA extractions were performed for each of the 45 tank water samples collected before and after pasteurization. In order to extract total genomic DNA from the tank water samples (950 mL) a modified version of the boiling method was utilized (Watterworth et al., 2005) as outlined in Ndlovu et al. (2015). Once DNA extractions had been performed, genomic DNA and total DNA was visualized on a 0.8% agarose gel stained with 0.5 μg/mL ethidium bromide. Electrophoresis was conducted at 80 V for approximately one hour with the use of 1 × TBE buffer (Sambrook et al., 1989). 2.7. Genus specific PCR reactions Primers and PCR conditions as outlined in Dobrowsky et al. (2014) were utilized in the current study for the identification of bacteria

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commonly associated with harvested rainwater. Each PCR mix was performed in a final volume of 50 μL. For the detection of Shigella spp., Salmonella spp. and Aeromonas spp. the PCR mix consisted of 10 μL of 5 × Green GoTaq® Flexi Buffer (1×) (Promega), 4 μL MgCl2 (2.0 mM) (Promega), 0.5 μL of each dNTP (0.1 mM) (Thermo Scientific), 0.5 μL of the respective PCR primers (0.1 μM), 0.3 μL of GoTaq® Flexi DNA Polymerase (Promega) (1.5U) and 10 μL of template DNA. For Yersinia spp. and Klebsiella spp. the same PCR mix was used with the exception that 1.5 μL of the respective forward and reverse PCR primers (0.3 μM) was used. For Pseudomonas spp. and Legionella spp., again, the same reaction mixture was used, however 2.0 and 2.5 μL of each PCR primer (0.4 and 0.5 μM, respectively) was used, respectively. A positive and a negative control were included for each of the PCR assays, as outlined in Dobrowsky et al. (2014). All PCR products were analyzed by gel electrophoresis in 1.2% agarose (Bio-Rad) containing 0.5 μg/mL ethidium bromide in 1 × TBE buffer. Deoxyribonucleic acid bands were confirmed by UV illumination and photographed using the Gel Doc 1000 documentation system (BioRad). Once the size of the PCR products had been confirmed, products of representatives of the samples were purified and concentrated using the DNA Clean & Concentrator™-5 Kit (Zymo Research) as per manufacturer's instructions. The cleaned products were then sent to the Central Analytical Facility at Stellenbosch University for sequencing. Chromatograms of each sequence were examined using FinchTV version 1.4.0 software and were aligned using DNAman™ version 4.1.2.1 software. Sequence identification was completed using the National Centre for Biotechnology Information (NCBI) and The Basic Local Alignment Search Tool (BLAST) (http://blast.ncbi.nlm.nih.gov/Blast.cgi) to find the closest match of local similarity between isolates and the international database in GenBank, EMBL, DDBJ and PDB sequence data (Altschul et al., 1990). The sequences of representative isolates, which indicated N 97% similarity (b3% diversity) to organisms on the database, were recorded as a positive result. 2.8. Statistical analysis The data obtained was assessed using the statistical software package Statistica™ Ver. 11.0 (Stat Soft Inc., Tulsa, USA). For evenly distributed data ANOVA analysis was performed to test the significance of the data set. In all tests a P-value smaller than 0.05 was considered as statistically significant (Dunn and Clark, 1974). 3. Results

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3.2. Chemical analysis Cations analyzed were within the drinking water guidelines according to SANS 241 (South African Bureau of Standards, SABS, 2005), Department Of Water Affairs and Forestry (DWAF) (1996), ADWG (NHMRC and NRMMC., 2011) and World Health Organization (WHO) (2011), with the exception of iron, nickel, aluminum and lead as represented in Table 2. The Department Of Water Affairs and Forestry (DWAF) (1996) guidelines stipulate that iron should not exceed 100 μg/L and only one tank water sample (collected before pasteurization at 55 °C) was within the Department Of Water Affairs and Forestry (DWAF) (1996) guidelines for iron, with iron ranging from the lowest concentration of 113.4 μg/L (before pasteurization at 65 °C) to the highest concentration of 441.99 μg/L (before pasteurization at 91 °C). In addition, two samples were not within the SANS 214 guidelines for iron (200 μg/L), namely the sample collected after pasteurization at 65 °C (218.22 μg/L) and the water sample collected before pasteurization at 91 °C (441.99 μg/L), which also exceeded the ADWG guideline of 300 μg/L for iron. The ADWG (NHMRC and NRMMC., 2011) guidelines stipulate that nickel should not be above 20 μg/L and while all the samples collected before pasteurization and after pasteurization at 91 °C were within the ADWG, samples collected after pasteurization at 55 °C, 65 °C and 78 °C were not within standards and were recorded at 46.43 μg/L, 22.94 μg/L and 32.82 μg/L, respectively. The concentration of nickel in all the tank water samples, were however within the stipulated standards of the SANS 241 (South African Bureau of Standards, SABS, 2005) and World Health Organization (WHO) (2011) of 150 μg/L and 70 μg/L, respectively. The aluminum concentrations of all the collected tank water samples were within the drinking water guidelines as stipulated by SANS 241 (South African Bureau of Standards, SABS, 2005), Department Of Water Affairs and Forestry (DWAF) (1996), ADWG (NHMRC and NRMMC., 2011) and World Health Organization (WHO) (2011). The average concentration of tank water samples collected after pasteurization at 78 °C, however, exceeded the ADWG (NHMRC and NRMMC., 2011) of 100 μg/L, with an average concentration of 130.98 μg/L recorded. The concentration of lead in drinking water should not exceed 10 μg/L according to Department Of Water Affairs and Forestry (DWAF) (1996), the ADWG (NHMRC and NRMMC., 2011) and World Health Organization (WHO) (2011). However, three samples collected after pasteurization at 55 °C, 78 °C and 91 °C exceeded these guidelines with average concentrations of 12.81 μg/L, 17.20 μg/L and 13.2 μg/L recorded in the respective tank water samples. These concentrations were however, still within the SANS 241 (South African Bureau of Standards, SABS, 2005) guideline of 20 μg/L.

3.1. Physico-chemical parameters The dates the samples were collected from the solar pasteurization system, the temperatures of the untreated (before pasteurization) and treated tank water samples (after pasteurization) as well as the average ambient temperatures are recorded in Table 1. An overall average pH of 6 was measured for all tank water samples, collected before and after pasteurization. The temperature of the water samples collected from the RWH tank ranged from the lowest temperature of 17 °C (11.07.2013) to the highest recorded temperature of 24 °C on two sampling days (26.08.2013 and 02.09.2013). The lowest total rainfall throughout the sampling period was recorded for October (39.6 mm per month). At the start of the sampling period, rainfall was recorded at 169.6 mm per month in July 2013, which then increased to 371.6 mm per month in August 2013 and decreased again in September 2013 (177.2 mm per month). An average of 61 °C and a range of 34 °C (lowest) to 98 °C (highest) was obtained for the temperature of the pasteurized tank water samples monitored by the log tagger. By monitoring the temperature inside the storage tank of the pasteurization unit, for one month, it was determined that the system remained at the temperature ranges of 55 to 57 °C, 64 to 66 °C, 72 to 74 °C, 78 to 81 °C and 90 to 91 °C for 2.32, 2.15, 1.76, 1.77 and 0.62 h, respectively.

Table 1 The daily ambient temperatures and the temperatures of the untreated and treated rainwater samples on the sampling dates. Sampling date

Temperature of untreated rainwater (°C)

Temperature of treated rainwater (°C)

Ave. daily ambient temperature (°C)

11.07.2013 22.07.2013 30.07.2013 19.08.2013 20.08.2013 26.08.2013 02.09.2013 06.09.2013 06.09.2013 10.09.2013 10.09.2013 11.09.2013 11.09.2013 12.09.2013 09.10.2013

17 18 20 19 23 24 24 20 22 22 22 19 20 21 22

56 57 65 55 81 78 64 81 91 66 74 72 90 91 73

27.1 20.8 21.3 21.3 19.09 19.7 21.1 22.9 22.9 15.8 15.8 17 17 20 29.4

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Table 2 Cation concentrations obtained from the unpasteurized and duplicate pasteurized rainwater samples collected at various temperatures that were compared to the recommended concentrations as stipulated by the respective drinking water guidelines (n = 12). Metal

Before 55 °C

After 55 °C

Before 65 °C

After 65 °C

Before 78 °C

After 78 °C

Before 91 °C

After 91 °C

SANS 241

DWAF

ADWG

WHO

Boron as B (mg/L) Calcium as Ca (mg/L) Potassium as K (mg/L) Magnesium as Mg (mg/L) Sodium as Na (mg/L) Aluminum as Al (μg/L) Chromium as Cr (μg/L) Manganese as Mn (μg/L) Iron as Fe (μg/L) Cobalt as Co (μg/L) Nickel as Ni (μg/L) Copper as Cu (μg/L) Zinc as Zn (μg/L) Arsenic as As (μg/L) Selenium as Se (μg/L) Molybdenum as Mo (μg/L) Cadmium as Cd (μg/L) Antimony as Sb (μg/L) Barium as Ba (μg/L) Mercury as Hg (μg/L) Lead as Pb (μg/L)

0 3.72 0.28 0.42 3.32 9.4 0.00 1.20 70.59 0.03 0.29 4.15 46.60 0.15 0.79 0.00 0.01 0.02 28.93 0.04 0.09

0.22 6.86 0.56 0.95 5.58 61.14 0.39 15.68 195.59 0.64 46.43 43.57 338.73 0.64 1.77 0.00 0.13 0.14 36.29 0.03 12.81

0.00 5.03 0.27 0.49 3.20 16.0 0.2 0.1 113.4 0.0 0.4 6.6 9.1 0.4 3.7 0.03 0.0 0.1 11.5 0.1 0.8

0.00 7.14 0.49 0.96 5.34 44.81 0.25 13.67 218.22 0.35 22.94 19.56 316.97 0.55 1.80 0.02 0.17 0.20 25.93 0.12 3.86

0.00 4.07 0.38 0.44 3.33 15.08 0.18 12.13 182.71 0.10 1.04 29.34 57.67 0.22 0.79 0.00 0.06 0.08 41.12 0.01 2.46

0.26 7.00 0.54 0.93 5.57 130.98 0.36 13.14 179.08 0.50 32.82 59.56 276.62 0.41 2.36 0.00 0.19 0.18 35.95 0.02 17.20

0.01 4.56 0.31 0.46 2.91 4.86 0.30 12.77 441.99 0.19 1.88 23.75 39.64 0.33 1.02 0.04 0.02 0.14 61.79 0.03 1.06

0.11 4.58 0.32 0.50 3.14 48.8 0.3 8.4 170.1 0.3 16.0 71.7 171.8 0.4 0.7 0.0 0.1 0.1 39.5 0.0 13.2

– 150 50 70 200 300 100 100 200 500 150 1000 5000 10 20 – 5 – – 1 20

– 200 50 30 100 150 50 50 100 – – 1000 3000 10 20 – 5 – – 1 10

4 200 – 200 180 100 50 500 300 – 20 2000 3000 10 10 50 2 3 2000 1 10

2.4 – – – – – 50 – – – 70 2000 – 10 40 – 3 20 700 6 10

All anions were within drinking water guidelines (unpasteurized and pasteurized rainwater samples) according to SANS 241 (South African Bureau of Standards, SABS, 2005), Department Of Water Affairs and Forestry (DWAF) (1996), ADWG (NHMRC and NRMMC, 2011) and World Health Organization (WHO) (2011). At higher pasteurization temperatures of 78 °C and 91 °C the concentrations of sulfate increased and chloride concentrations increased after pasteurization at 55 °C (from 7.2 mg/L to an average of 12 mg/L) and 65 °C (from not being detected to an average of 11 mg/L). A decrease in the concentration of chloride was however, observed after pasteurization at 78 °C from 7.2 mg/L to an average of 3.1 mg/L. No significant change in concentrations was observed for nitrate and nitrite, phosphate and fluoride in the tank water samples after pasteurization for all temperatures (55 to 91 °C).

3.3. Indicator bacteria detected in untreated and solar pasteurized water samples At each pasteurization temperature an untreated and duplicate treated tank water samples were collected and analyzed for the presence of indicator bacteria. All total coliforms and E. coli numbers enumerated after the pasteurization treatment, ranging from temperatures of 55 to 57 °C up to 90 to 91 °C, were reduced to below the detection limit and were within the Department Of Water Affairs and Forestry (DWAF) (1996) guidelines (Fig. 2). However the heterotrophic plate count (HPC) was above the Department Of Water Affairs and Forestry (DWAF) (1996) guidelines for the temperature ranges of 55 to 57 °C (average 5.5 × 105 CFU/mL) and 64 to 66 °C (average 4.5 × 105 CFU/mL), with

Fig. 2. Indicator bacteria enumerated from pasteurized rainwater samples collected at various temperatures and corresponding duplicate unpasteurized rainwater samples.

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the HPC below the detection limit after solar pasteurization at the temperature range of 72 to 91 °C (Fig. 2). 3.4. Genus specific PCR detection of bacteria commonly identified in harvested rainwater Untreated tank water samples as well as the tank water samples treated at various temperatures (Table 1) by solar pasteurization, were screened using PCR assays for the detection of various bacteria commonly associated with harvested rainwater. The percentages of the various bacterial genera present in the untreated rainwater and the pasteurized tank water samples and the pasteurization temperature ranges, where the PCR assays tested positive, are summarized in Fig. 3. No Salmonella spp. were detected in any of the tank water samples analyzed, while Aeromonas spp. (GenBank accession no. CP005966.1) were only detected in the untreated tank water samples. Shigella spp. (GenBank accession no. HE616529.1) were only detected in the tank water samples solar pasteurized at temperatures of 55 to 57 °C, with Klebsiella spp. (GenBank accession no. AF303617.1) detected in the temperature ranges of 55 to 57 °C, 64 to 66 °C and 72 to 74 °C. Yersinia spp. (GenBank accession no. HM142628.1) were detected at all the temperature ranges with the exception of 72 to 74 °C and 90 to 91 °C. In contrast, Legionella spp. (GenBank accession no. KC209485.1, AB858005.1, KC209446.1) and Pseudomonas spp. (GenBank accession no. JX279939.1; KF260975.1; KF561877.1) were detected at all the temperature ranges analyzed. 3.5. Determining the maximum volume of rainwater harvested from the solar pasteurization system In order to calculate the amount of pasteurized tank water produced by the solar system, the energy output of one evacuated tube, utilized in the closed coupled solar system was calculated at 50 W (personal communication). As 12 evacuated tubes were connected to the storage tank of the pasteurization system, the amount of thermal energy (Q) was calculated at 600 W which could be converted to 2160 kJ/h (3.6 MJ = 1 kWh). Given the specific heat (Cp) of water (4.2 Jkg− 1 °C−1), the amount of pasteurized water produced (m) could be calculated by substituting the input and output temperatures as described in Table 1, into Eq. (3b). At irradiation values of 1000 W/m2, with a 30% solar energy conversion rate and at an average of 6 h per day of sunshine, the average quantity of pasteurized tank water produced for the 55–57 °C, 64–66 °C, 72–74 °C, 78–81 °C, 90–91 °C temperature ranges, was calculated at 13.6 kg/h, 12.0 kg/h, 9.90 kg/h, 8.94 kg/h and 7.38 kg/h, respectively.

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4. Discussion A heat-based disinfection system, namely a closed-coupled system was analyzed for its efficiency to treat roof harvested rainwater directly from a RWH tank. Chemical analysis indicated that all cations and anions (with the exception of iron, aluminum, lead and nickel) present in both the unpasteurized and pasteurized water at the varying temperature ranges analyzed, were within the drinking water guidelines according to SANS 241 (South African Bureau of Standards, SABS, 2005), Department Of Water Affairs and Forestry (DWAF) (1996), ADWG (NHMRC and NRMMC., 2011) and World Health Organization (WHO) (2011). Concentrations of the cations, aluminum, lead and nickel were shown to increase significantly (p b 0.05) after pasteurization at the various temperature ranges. During pasteurization, the rainwater is in direct contact with borosilicate glass collector tubes and the main stainless steel storage tank. As the composition of stainless steel may vary from 50–88% iron, 11 to 30% chromium, and 0–31% nickel, researchers have shown that during simulated cooking processes, nickel and iron leaches from stainless steel cooking ware into food (Kuligowski and Halperin, 1992; Kamerud et al., 2013). In a study conducted by Semwal et al. (2006) aluminum also leached from stainless steel cooking utensils during food preparation. Therefore it is hypothesized that the iron, aluminum, lead and nickel may have leached from the stainless steel storage tank into the rainwater during the current study. In order to provide thermal stability, mechanical strength, and potentially chemical resistance, it is recommended that the storage tank of the pasteurization system be manufactured from an alternative material, such as high density polyethylene (HDPE), which is able to withstand the high temperatures, yet will not negatively influence the quality of harvested rainwater. A company in Stellenbosch, Crest (http://www.solapool.co.za/index.html), is thus currently developing a solar pasteurization system with a storage tank that will be manufactured from a high density based polyethylene. While heterotrophic bacteria still persisted at the 55 to 57 °C and 64 to 66 °C temperature ranges, total coliform, E. coli and heterotrophic bacteria counts were reduced to below the detection limit (≥ 99%) in the tank water samples pasteurized at the 72 to 74 °C, 78 to 81 °C and 90 to 91 °C temperature ranges (Fig. 2). In the current study the heterotrophic bacteria were reduced by 91% at temperatures ranging from 55 to 66 °C and from temperatures of 72 °C upward, a ≥ 99% reduction in heterotrophic bacteria was observed. However, total coliform and E. coli numbers were reduced by ≥99%, with total coliforms and E. coli below the detection limit from 55 °C. Spinks et al. (2006) suggested that water temperatures should reach between 55 and 65 °C in order to eliminate enteric pathogenic bacteria. Other studies have suggested that temperatures below boiling greatly reduce bacterial numbers from tank water samples resulting in water quality that is within the

Fig. 3. The percentage of unpasteurized rainwater and duplicate pasteurized rainwater samples that tested positive for various bacterial genera and the corresponding pasteurization temperature ranges.

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Australian Drinking Water Guidelines (Lye, 1991; Coombes et al., 1999, 2003). The indicator bacteria counts obtained in the current study, when compared to the various drinking water guidelines, the minimum temperature required to treat harvested rainwater is 72 °C. In a similar study, Jørgensen et al. (1998) recommended that a temperature of 75 °C be utilized to decontaminate river water utilizing a flow-through system of copper pipes. Moreover, Jørgensen et al. (1998) reported that bacteria including Salmonella typhimurium, Streptococcus faecalis and E. coli were inactivated at temperatures of 65 °C and above. However, Jørgensen et al. (1998) utilized standard culturing methods, including membrane filtration, for the enumeration of bacteria, which may not have accounted for the bacteria that may enter into a viable but nonculturable state (VBNC). Many studies have indicated that microorganisms may occur in a VBNC form in water samples (Colwell et al., 1985; Oliver, 2005, 2010), and therefore standard culturing methods may allow for false negatives. Microorganisms including Aeromonas spp., Klebsiella spp., Legionella spp., Pseudomonas spp., Salmonella spp. and Shigella spp., have also been reported to enter a viable but nonculturable state (Oliver, 2010). The current study thus indicated that, based on genus specific PCR analysis utilized to screen pasteurized tank water samples for the presence of bacteria that have previously been detected in harvested rainwater, Yersinia spp., Legionella spp. and Pseudomonas spp. were detected in the tank water samples pasteurized at the higher temperature ranges of 78 to 81 °C, while Legionella spp. and Pseudomonas spp. were still detected at the temperature range of 90 to 91 °C. As this was a preliminary study, the viability of these organisms however, was not verified and of the many pitfalls associated with PCR detection methods, it is known that PCR based assays cannot distinguish between viable and non-viable organisms (Ahmed et al., 2013). However, in a study conducted by Reyneke et al. (unpublished results) the BacTiter-Glo™ Microbial Cell Viability Assay (Promega, Madison, WI, USA) was utilized to measure the quantity of ATP produced in the form of relative light units (RLU) in tank water samples. The amount of ATP produced indicated the presence/absence of viable microbial cells in unpasteurized tank water samples and corresponding pasteurized tank water samples that were collected at the temperature ranges of 70 to 79 °C, 80 to 89 °C and 90 to 95 °C. Results indicated that although a significant decrease in RLU (N94%) was observed for pasteurized tank water samples compared to unpasteurized tank water samples, RLU were still detected at the temperature ranges of 70 to 79 °C (7.2 × 103 RLU/100 μL), 80 to 89 °C (1.9 × 103 RLU/100 μL) and 90 to 95 °C (6.9 × 102 RLU/100 μL). These results, therefore, indicate the viability of organisms at pasteurization temperatures of above 78 °C and that potential pathogens including Legionella spp., Pseudomonas spp. and Yersinia spp. may still be viable at the high pasteurization temperatures. Thus to confirm the viability of the particular pathogenic organisms (Legionella spp., Pseudomonas spp. and Yersinia spp.), detected in tank water samples pasteurized at temperatures greater than 72 °C, whole sample quantitative analysis, including viability quantitative PCR (qPCR), should be conducted. The ADWG (NHMRC and NRMMC., 2011) does not stipulate a guideline for the detection of Legionella, however, it is noted by the ADWG that hot water systems may allow for the proliferation of Legionella spp. and this may pose a serious human health risk. Legionella have also been detected in different water sources including man-made warm water systems such as cooling towers, hot tubs, showerheads and spas (Fields, 1996; Fields et al., 2002). In the environment, Legionella exist as free living bacteria, within living protozoa or within aquatic biofilms and have been detected in environmental samples by culture methods (40%) and PCR assays (80%; Fields et al., 2002). Legionella, via the inhalation of infected aerosols, have been known to cause an acute form of pneumonia as part of a multisystem disease known as Legionnaires' disease (also referred to as Legionellosis or Legion Fever) (Fraser et al., 1997) or a milder form of pulmonary infection known as Pontiac fever which is a flu like illness (Glick et al., 1978). Moreover, although a drinking water health guideline has not been stipulated by

the ADWG (NHMRC and NRMMC., 2011) for Pseudomonas spp., the guidelines do, however, recognize the presence of Pseudomonas in water systems as being an indicator of poor bacteriological quality. Pseudomonas have been isolated and detected from a number of environments including vegetables (Uzeh et al., 2009), feces (NHMRC and NRMMC., 2011), soil (Nawab et al., 2003), river water (Kang and Kondo, 2002) and rainwater (Dobrowsky et al., 2014). Pseudomonas spp. includes the medically important opportunistic pathogen P. aeruginosa, which is associated with urinary tract and nosocomial infections (Gilardi, 1972; Ferroni et al., 1998). In addition, the ADWG indicate that if Yersinia spp. are “explicitly sought, pathogenic Yersinia spp. should not be detected.” Yersinia spp. have been isolated from a number of environmental samples including various water sources, however, domestic and wild animals have been suggested as possible reservoirs for Yersinia spp. (NHMRC and NRMMC., 2011). Three species of Yersinia are known to cause disease in humans and these include Y. pestis, Y. pseudotuberculosis and Y. enterocolitica (Rosqvist et al., 1991). Yersinia pestis is well known to have caused plague, a collective term used for systemic invasive infectious diseases (Parkhill et al., 2001), and infects the lymph nodes of humans or rodents resulting in bacteremia with necrotic and hemorrhagic lesions in organs (Meyer, 1965). The performance of solar pasteurization systems has been reported utilizing different methods, for example in l/h-m2, l/m2-day or kg/h (Duff and Hodgson, 2005). In this study, at lower the lower temperature ranges (55–57 °C, 64–66 °C) the solar pasteurization system could produce 13.6 kg/h and 12.0 kg/h, and when the temperatures increased to 72–74 °C, 78–81 °C and 90–91 °C, the quantity of pasteurized tank water decreased to 9.90 kg/h, 8.94 kg/h and 7.38 kg/h, respectively. Many studies have thus indicated the use of thermostat valves to control the release of treated water at a predetermined temperature (Andreatta et al., 1994; Anderson, 1996; Jørgensen et al., 1998; Abraham et al., 2015). For example, Stevens et al. (1998) utilized an automotive thermostat to control the flow of water at 75 °C; the flat plate solar water pasteurizer was cable of treating 55 l/h-m2. However, of the many pitfalls associated with the use of thermostat valves in many instances water that has not been adequately treated may pass through the valve (Duff and Hodgson, 2005). However, as the purpose of the study is to provide treated water to individuals, a mechanism to control the release of treated water should be investigated in future studies. There are a few factors that may influence the quality of the harvested rainwater and these should be considered when selecting a storage tank as well as the appropriate design of the harvesting and storage system. These factors include the desired area, together with the topography, the weather conditions, the proximity to pollution sources, the type of catchment area, the type of water tank and the handling and management of the water harvesting system (Gould, 1999; Zhu et al., 2004; Sazakli et al., 2007). The results of this study thus indicated that the pasteurization system employed may, in future, provide treated rainwater (N72 °C) for drinking and domestic purposes at the average sized household level (up to four people), if further studies are to be conducted to confirm that the harvested rainwater has been adequately treated. 5. Conclusions The efficiency of a solar pasteurization system in treating harvested rainwater was investigated. Chemical analysis indicated that all cations and anions present in both the unpasteurized and pasteurized water were within the respective drinking water guidelines with the exception of iron, aluminum, lead and nickel. These four cations were shown to increase significantly after pasteurization at various temperatures and it is hypothesized that these elements could have leached from the stainless steel storage tanks of the pasteurization system. Future studies should thus investigate the effect of pasteurization on the chemical quality of rainwater using a pasteurization system that will not corrode during high temperature exposure. Microbial analysis indicated that

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rainwater samples pasteurized at 72 °C and above (78–81 °C and 90–91 °C) could be utilized for potable purposes as total coliforms, E. coli and HPC were reduced to zero. However, PCR analysis of the pasteurized rainwater samples for the presence of pathogenic bacteria at the various temperature ranges indicated that Legionella spp. and Pseudomonas spp. persisted even at the temperature range of 90 to 91 °C. Although conventional PCR confirmed the presence of DNA of certain pathogenic bacteria, further studies are required to confirm the viability of specific bacterial pathogens at higher pasteurization temperatures (greater than 72 °C). Based on the results obtained in the current study rainwater harvesting tanks may be accompanied by the installation of a solar pasteurization system (that does not corrode) as a treatment system to provide potable water and water for other domestic purposes. Throughout the year, including the winter months, solar pasteurization may provide adequate volumes of treated rainwater for drinking and domestic purposes. The duration at which the tank water will remain at elevated temperatures inside the storage tank of the pasteurization unit will thus depend on many factors, for example, how often tank water samples are collected from the system, the amount of UV exposure and the ambient temperature measured on a particular day. Moreover, in agreement with Mwenge Kahinda et al. (2007), the type and capacity of the domestic rainwater harvesting system to be installed, should depend on each community, as variables such as winter or summer rainfall may affect the management of the treatment systems. However, this was a preliminary study and pilot scale RWH systems, including solar pasteurization treatment systems, are currently being constructed on site in a local informal settlement. An operational manual as well as a pamphlet guide outlining factors such as, cleaning practices of the catchment areas, tank maintenance and the handling and management of the water harvesting system, will thus be disseminated to the primary users of the RWH treatment systems. In addition, the tank water quality as well as the general daily water usage will be monitored.

Acknowledgments The authors would like to thank the Water Research Commission (Grant number: K5/2368//3) and the National Research Foundation of South Africa (Grant number: 90320) for funding this project. Lastly the authors would like to thank Mr. Willem van Kerwel and the Welgevallen Experimental Farm of Stellenbosch University (South Africa) for the permission to set-up the RWH tanks and the treatment systems on the farm and for their assistance during the trails. The South African Weather Services is thanked for providing rainfall data.

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