Sustainable point-of-use solar disinfection system for roof-harvested rainwater treatment

Strauss, Andre (2018-03)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Numerous countries worldwide, particularly in sub-Saharan Africa, are currently experiencing severe water shortages and drought conditions. Domestic rainwater harvesting (DRWH) has thus been earmarked as an alternative water source that could provide water directly to households. However, research has indicated that the microbial quality of rainwater is sub-standard and does not comply with drinking water standards as established by various water associations. It is thus recommended that roof-harvested rainwater should be treated prior to use for potable purposes. While the implementation of a first flush (FF) diverter as part of a DRWH system improves the microbial quality of roof-harvested rainwater, cost-effective primary treatment methods such as solar disinfection (SODIS) still need to be implemented on-site to significantly reduce the microbial load (Chapter one). The primary aim of Chapter two was thus to design and construct a pilot-scale SODIS batch system fitted with a compound parabolic collector (CPC) which was (i) constructed from cost-effective materials; (ii) robust in nature in order to withstand adverse environmental conditions and (iii) required minimum maintenance. Two SODIS-CPC systems were constructed and connected to two separate rainwater harvesting tanks. One rainwater harvesting tank was utilised without pre-treatment, while the second tank was connected to a FF diverter. To determine the efficiency of the SODIS-CPC systems, the chemical (anion and cation concentrations as well as turbidity and water hardness) and the microbial quality [indicator organisms including Escherichia coli (E. coli), hetero-trophic plate counts (HPC), enterococci, total and faecal coliforms] of untreated and SODIS treated rainwater samples were assessed during seven sampling events. In addition, the viable Legionella and Pseudomonas population present in the untreated and SODIS treated rainwater was determined using ethidium monoazide bromide quantitative polymerase chain reaction (EMA-qPCR) assays. Chemical analysis indicated that both the anion and cation concentrations before [Tank 1 and Tank 2 (FF)] and after SODIS treatment [SODIS-CPC-1 and SODIS-CPC-2 (FF)] were within the drinking water standards as stipulated by various national and international water associations. In addition, the turbidity of all untreated and SODIS treated rainwater samples were within the aesthetic drinking water guideline, while the total water hardness of all samples were classified as soft. Microbial analysis further indicated that the microbiological quality of the untreated rainwater [Tank 1 and Tank 2 (FF)] was compromised as E. coli, HPC and total coliforms were detected at concentrations exceeding drinking water guidelines. However, after SODIS treatment, the E. coli and HPC were reduced to within the drinking water guidelines. In contrast, while total coliforms were reduced to within the drinking water guidelines during sampling sessions 1 to 4, counts exceeding the guidelines were obtained in the treated samples collected during sampling sessions 5 to 7 for both SODIS-CPC-1 and SODIS-CPC-2 (FF) systems. Moreover, viable Legionella spp. and Pseudomonas spp. were detected in the Tank 1 and Tank 2 (FF) rainwater samples. The copy numbers of these organisms then decreased significantly (p < 0.05) after SODIS treatment in the SODIS-CPC-1 rainwater samples. However, while both Legionella spp. and Pseudomonas spp. copy numbers decreased after treatment in the SODIS-CPC-2 (FF) system, the decrease was not significant (p = 0.195). As results indicated that opportunistic pathogenic genera (Legionella spp. and Pseudomonas spp.) were still viable after SODIS treatment, the primary aim of Chapter three was to investigate the overall diversity and abundance of the viable bacterial community present in the Tank 1 rainwater and the SODIS-CPC-1 treated rainwater, using Illumina next generation sequencing coupled with EMA. Using this technique, the viable opportunistic pathogenic genera persisting after SODIS treatment in roof-harvested rainwater were also detected and identified. After taxonomic assignments were performed, various α-diversity indices were utilised to investigate the diversity and abundance of the viable bacterial communities present in the untreated versus SODIS treated rainwater. Results indicated that there was a significant reduction (p = 0.0033) in species richness after SODIS treatment, indicating that the number of different species in SODIS-CPC-1 rainwater samples were less than in the Tank 1 rainwater samples. In addition, the Shannon diversity index significantly decreased (p = 0.0107) after SODIS treatment, indicating that the species in the SODIS-CPC-1 rainwater samples were less diverse than in the Tank 1 rainwater samples and that the treated rainwater samples were possibly dominated by a smaller group of viable bacteria. The β-diversity was further determined using the Bray-Curtis distance metric and permutational multivariate analysis of variance (PERMANOVA), whereafter results indicated that there was a significant (p < 0.05) shift in the viable bacterial community after SODIS treatment. Although the Nocardiaceae family and Rhodococcus genus dominated the Tank 1 (16.5 %) and SODIS-CPC-1 rainwater samples (44.0 %), the rest of the viable bacterial community differed. For example, Pseudomonadaceae (8.9 %) was the second most abundant family, followed by Sphingomonadaceae (6.0 %) in the Tank 1 rainwater samples. While in the SODIS-CPC-1 rainwater samples, Micrococcaceae (31.7 %) was the second most abundant family, followed by Oxalobacteraceae (5.0 %). Furthermore, signatures of opportunistic pathogenic genera were detected in both the Tank 1 and SODIS-CPC-1 rainwater samples. In addition, genera such as Pseudomonas, Clostridium sensu stricto, Legionella, Mycobacterium and Yersinia, amongst others, were detected in rainwater samples after SODIS treatment. It was thus hypothesised that the presence of these potential opportunistic pathogenic genera may be ascribed to debris, leaves, soil, dust and bird faecal matter which contaminated the catchment area either by anthropogenic activity or naturally through wind dispersion, etc. Based on the results obtained in the current study, it is highly recommended that the catchment area is regularly cleaned, particularly before the rainy season commences and that a FF diverter is routinely installed as part of a RWH system. In addition, it is recommended that the SODIS treated rainwater should primarily be used for domestic purposes such as laundry, irrigation, car washing, etc.

AFRIKAANSE OPSOMMING: Talle lande wêreldwyd, veral in sub-Sahara Afrika, word tans geteister deur ernstige watertekorte en droogtes. Huishoudelike reënwater-oesting (RWO) is dus ten toon gestel as 'n alternatiewe waterbron wat water direk aan huishoudings kan voorsien. Navorsing het egter aangedui dat die mikrobiese kwaliteit van reënwater nie voldoen aan die drinkwaterriglyne soos vasgestel deur verskeie waterverenigings nie. Daar word dus aanbeveel dat dak-opgevange reënwater vooraf behandel moet word indien dit vir drink doeleindes aangewend word. Terwyl die implementering van 'n eerste spoel (ES) -afleier as deel van 'n RWO-stelsel die mikrobiese kwaliteit van dak-opgevange reënwater verbeter, moet koste-effektiewe behandelingsmetodes soos sonlig-disinfeksie (SODIS) geïmplementeer word om die mikrobiese lading beduidend te verminder (Hoofstuk een). Die doel van hoofstuk twee was dus om 'n kleinskaalse SODIS-stelsel te ontwerp en te bou wat toegerus is met 'n saamgestelde paraboliese versamelaar (SPV) wat (i) uit koste-effektiewe materiale gebou is; (ii) robuus van aard is om uiterse omgewingstoestande te weerstaan en (iii) wat minimum instandhouding vereis. Twee SODIS-SPV stelsels is gebou en gekoppel aan twee afsonderlike reënwater tenke. Een reënwater tenk is gebruik sonder voorafbehandeling, terwyl die tweede tenk aan 'n ES-afleier gekoppel was. Die effektiwiteit van die SODIS-SPV-stelsels was bepaal deur die chemiese (anioon- en katioonkonsentrasies sowel as troebelheid en waterhardheid) en die mikrobiese kwaliteit [indikator organismes insluitend Escherichia coli (E. coli), heterotrofiese plate tellings (HPT), enterococci, totale en fekale koliforme], van onbehandelde en SODIS-behandelde reënwater-monsters te meet, gedurende sewe monsternemingsessies. Daarbenewens was die aantal lewensvatbare Legionella- en Pseudomonas spp. wat in die onbehandelde en SODIS behandelde reënwater voorkom, bepaal deur gebruik te maak van etidium monoazied bromied kwantitatiewe polimerase kettingreaksie (EMB-kPKR) analises. Chemiese analise het aangedui dat beide die anioon- en katioonkonsentrasies voor [Tenk 1 en Tenk 2 (ES)] en na SODIS-behandeling [SODIS-SPV-1 en SODIS-SPV-2 (ES)] binne die drink-waterriglyne was soos gestipuleer deur verskeie waterverenigings. Daaropvolgend het resultate getoon dat die troebelheid van alle onbehandelde en SODIS behandelde reënwater-monsters binne die estetiese drinkwaterriglyn was, terwyl die totale waterhardheid van alle monsters as ‘sag’ geklassifiseer is. Mikrobiese analises het verder aangedui dat die mikrobiologiese kwaliteit van die onbehandelde reënwater [Tenk 1 en Tenk 2 (ES)] ongeskik is vir drink doeleindes aangesien E. coli, HPT en totale koliforme opgespoor is by konsentrasies wat drinkwaterriglyne oorskry. Na die SODIS behandeling is E. coli en HPT egter verminder tot binne die drinkwaterstandaarde. In teenstelling, terwyl die totale koliforme verminder is tot binne die drinkwaterriglyne gedurende monsterneming-sessies 1 tot 4, het die koliforme telling, van beide SODIS-SPV-1 en SODIS-SPV-2 (ES) sisteme gedurende monsterneming-sessies 5 tot 7, die drinkwaterriglyne oorskry. Verder was lewensvatbare Legionella en Pseudomonas spp. opgespoor in Tenk 1 en Tenk 2 (ES) reënwater-monsters. Die kopie-getalle van hierdie organismes het beduidend afgeneem (p < 0.05) na SODIS behandeling in die SODIS-SPV-1 reënwater-monsters. Alhoewel beide Legionella en Pseudomonas kopie getalle afgeneem het na SODIS behandeling in die SODIS-SPV-2 (ES) stelsel, was hierdie afname nie beduidend nie (p = 0.195). Aangesien resultate daarop dui dat opportunistiese patogeniese genera (Legionella spp. en Pseudomonas spp.) nog steeds lewensvatbaar was na SODIS behandeling, was die doel van Hoofstuk drie om die algehele diversiteit en oorvloedigheid van die totale lewens-vatbare bakteriese gemeenskap wat in beide Tenk 1 en SODIS-SPV-1 voorkom, te bepaal deur gebruik te maak van Illumina volgende generasie volgordebepaling gekoppel aan EMA. Met behulp van hierdie tegniek, is die lewensvatbare patogeniese en opportunistiese patogeniese genera wat voort leef na SODIS-behandeling van dak-opgevange reënwater, ook opgespoor en geïdentifiseer. Taksonomiese analises was uitgevoer deur verskeie α-diversiteitsindekse te gebruik om die diversiteit en oorvloedigheid van die lewensvatbare bakteriese gemeenskap, teenwoordig in die onbehandelde sowel as die SODIS-behandelde reënwater, te ondersoek. Resultate het aangedui dat daar 'n beduidende afname (p = 0.0033) was in spesierykheid na SODIS behandeling, wat daarop dui dat die aantal verskillende spesies in SODIS-SPV-1 reënwater-monsters minder was as in die Tenk 1 reënwater-monsters. Daaropvolglik, het die Shannon-diversiteitsindeks beduidend afgeneem (p = 0.0107) na SODIS-behandeling wat aandui dat die spesies in die SODIS-SPV-1 reënwater-monsters minder divers was as in die Tenk 1 reënwater-monsters en dat die behandelde reënwater-monsters moontlik gedomineer is deur 'n kleiner groep lewensvatbare bakterieë. Die β-diversiteit is verder bepaal met behulp van die Bray-Curtis-afstandmatriks en permutatiewe multi-variante ontleding van variansie wat aangedui het dat daar 'n beduidende (p < 0.05) verandering in die lewensvatbare bakteriese gemeenskap na SODIS-behandeling was. Alhoewel die Nocardiaceae familie en die Rhodococcus genus die Tenk 1 (16.5 %) en SODIS-SPV-1 reënwater-monsters (44.0 %) oorheers het, was daar `n verskil in die res van die lewensvatbare bakteriese gemeenskap. Byvoorbeeld, Pseudomonadaceae (8.9 %) was die tweede oorvloedigste familie, gevolg deur Sphingomonadaceae (6.0 %) in die Tenk 1 reënwater-monsters. In die SODIS-SPV-1 reënwater-monsters was Micrococcaceae (31.7 %) die tweede oorvloedigste familie, gevolg deur Oxalobacteraceae (5.0 %). Verder is opportunistiese patogeniese genera in beide Tenk 1 en SODIS-SPV-1 reënwater-monsters opgespoor. Daarbenewens was genera soos Pseudomonas, Clostridium sensu stricto, Legionella, Mycobacterium en Yersinia, onder andere, in die reënwater-monsters aangetref na SODIS-behandeling. Die teenwoordigheid van hierdie opportunistiese patogeniese genera kan moontlik toegeskryf word aan blare, stof en voëlfekale afval wat die opvang-gebied besoedel, moontlik a.g.v. menslike aktiwiteite of natuurlik deur windverspreiding, ens. Na afloop van die huidige studie, word dit sterk aanbeveel dat die opvanggebied gereeld skoongemaak word, veral voor die reënseisoen begin, en dat 'n ES-afgeleier geïnstalleer moet word as deel van die RWO-stelsel. Verder word dit aanbeveel dat die SODIS behandelde reënwater hoofsaaklik vir huishoudelike doeleindes gebruik word, soos wasgoed, besproeiing, motorwas, ens.

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