An investigation into the effect of inline coagulation and air scouring to minimize ultrafiltration membrane fouling

Thesis (MEng)--Stellenbosch University, 2020.ENGLISH ABSTRACT: The quality of raw water is an essential factor that determines the treatment technologies and level of treatment required to attain specified treatment objectives. Water utilities such as Rand Water currently use conventional water treatment processes to purify water to drinking water standards. However raw water quality had been gradually deteriorating due to agricultural and industrial activities and poorly performing wastewater treatment plants. Low-pressure membrane filtration processes such as microfiltration(MF) and ultrafiltration(UF) have become an attractive alternative treatment technology to replace or supplement conventional water treatment for surface waters, as they consistently produce drinking water of high quality. However, the major disadvantage of membrane filtration is membrane fouling. The objective of this study was to determine the effect of coagulant dosage, air scouring rate and the frequency of air scouring on the rate of membrane fouling and final water quality, for Vaal Dam raw water. The investigation into the effect of the polymeric coagulant dosage, air scouring rate and the frequency of air scouring on the rate of membrane fouling was conducted using a bench-scale outside-in hollow fibre PVDF submerged UF module. Firstly, ranges for polymeric coagulant dosage, air scouring rate, and the frequency of air scouring were selected and independently validated using an OFAT approach. These validated ranges were then used in a full factorial design of experiments (DoE). The purpose of conducting the DoE was to determine the combined effects of the factors and factors interactions on the rate of membrane fouling.In the scanning and validation investigation, the rate of membrane fouling reduced by 60% when the polymeric coagulant dosage was in the range of 1 to 8 mg/l, relative to no polymeric coagulant dosage. Excessive polymeric coagulant dosage increased the rate of membrane fouling. The rate of membrane fouling decreased with increasing air scouring rates range of 1 to 5 m3/m2.h. Air scouring rates above 5 m3/m2.h increased the rate of membrane fouling. The rate of membrane fouling reduced with increasing air scouring frequency from 0% to 100%. The air scouring frequency of 0% and 25% resulted in a similar rate of membrane fouling. Similarly, the air scouring frequency of 75% and 100% resulted in a similar rate of membrane fouling. The results from the DoE were analysed with statistical software and a regression model was obtained. This showed that 0 mg/l polymeric coagulant dosage and 10 min off / 10 min on air scouring frequency, irrespective of the air scouring rates resulted in the highest rate of membrane fouling. The treatment combination of 1 mg/l polymeric coagulant dosage, continuous air scouring resulted in the lowest rate of membrane fouling, irrespective of the air scouring rates. A Pareto plot indicated that the polymeric coagulant dosage, followed by the air scouring rate were the most critical factors in reducing the rate of membrane fouling. The frequency of air scouring had a moderate effect on the rate of membrane fouling, while the interaction of the air scouring rate and frequency of air scouring had a marginal effect.AFRIKAANSE OPSOMMING: Die kwaliteit van rouwater is ’n essensiële faktor wat die behandelingstegnologieë en vlak van behandeling benodig bepaalom gespesifiseerde behandelingsdoelwitte te bereik. Waterutiliteite soos Rand Water gebruik tans konvensionele waterbehandelingsprosesse om water na drinkbare waterstandaarde te suiwer. Rouwaterkwaliteit het egter geleidelik agteruitgegaan as gevolg van landbou-en industriële aktiwiteite en afvalwaterbehandelingsaanlegte wat swak presteer.Laedruk membraanfiltrasieprosesse soos mikrofiltrasie (MF) en ultrafiltrasie (UF) het ’n aantreklike alternatiewe behandelingstegnologie geword om konvensionele waterbehandeling vir oppervlakwater te vervang of aan te vul, omdat dit drinkwater van hoë kwaliteit konstant produseer. Die groot nadeel van membraanfiltrasie is egter membraanaanpakking. Die doel van hierdie studie was om die effek van koagulantdosering, lugskuurtempo en die frekwensie van lugskuring op die membraanaanpakking en finale waterkwaliteit vir die Vaaldam rouwater te bepaal. Die ondersoek om die effek van die polimeriese koagulantdosering, lugskuurtempo en die frekwensie van lugskuring op die tempo van membraanaanpakking is uitgevoer op ’n banktoetsskaal buitekant-binne hol vesel PVDF onderdompelde UF-module. Eerstens, die bestek vir polimeriese koagulantdosering, lugskuurtempo, en die frekwensie van lugskuring is gekies en onafhanklik gevalideer deur ’n OFAT-benadering te gebruik. Hierdie bestekke wat gevalideer is, is toe gebruik in ’n vol faktoriaalontwerp van eksperimente (DoE). Die doel van die uitvoering van die DoE was om die gekombineerde effekte van die faktore en faktorinteraksies op die tempovan membraanaanpakking te bepaal. In die skandering en validasie ondersoek, het die tempo van membraanaanpakking afgeneem met 60% wanneer die polimeriese koagulantdosering in die bestek van 1 tot 8 mg/l was, relatief tot geen polimeriese koagulantdosering. Oormatige polimeriese koagulantdosering het die tempo van membraanaanpakking laat toeneem. Die tempo van membraanaanpakking het afgeneem met toenemende lugskuurtempo’s in die bestek van 1 tot 5 m3/m2.h. Lugskuurtempo’s bo 5 m3/m2.h het die tempo van membraanaanpakking laat toeneem. Die tempo van membraanaanpakking het afgeneem met lugskuurfrekwensie wat toeneem van 0% tot 100%. Die lugskuurfrekwensie van 0% en 25% het ’n eenderse tempo van membraanaanpakking tot gevolg gehad. Op dieselfdemanier het die lugskuurfrekwensie van 75% en 100% ’n eenderse tempo van membraanaanpakking tot gevolg gehad.Die resultate van die DoE was geanaliseer met statistiese sagteware en ’n regressiemodel is verkry. Dit het getoon dat 0 mg/l polimeriese koagulantdosering en 10 min af/10 min aan vilugskuurfrekwensie, ongeag die lugskuurtempo’s, die hoogste tempo van membraanaanpakking tot gevolg gehad het. Die behandelingkombinasie van 1 mg/l polimeriese koagulantdosering, ononderbroke lugskuring, het die laagste tempo van membraanaanpakking tot gevolg gehad, ongeag die lugskuurtempo’s.’n Pareto-plot het aangedui dat die polimeriese koagulantdosering, gevolg deur die lugskuurtempo die mees kritiese faktore was in die verlaging van die tempo van membraanaanpakking. Die frekwensie van lugskuring het ’n gematigde effek op die tempo van membraanaanpakking gehad, terwyl die interaksie tussen die lugskuurtempo en frekwensie van lugskuring ’n marginale effek gehad het.Master

Evaluation of the Streaming Current Detector (SCD) for Coagulation Control

AbstractA streaming current detector (SCD) is an instrument for measuring the charge that exists on small, suspended particles in water. The SCD is the instrument that can be used to measure coagulated particle stability for the feedback control of coagulant dosage. This report discusses the application of SCD as an instrument for coagulation dosage control. The SCD with automatic control of coagulant dosage consistently produced acceptable water quality, even during periods of changing raw water turbidity and varying flow rates. It minimizes under and overdosing of coagulant. It requires regular cleaning and maintenance to ensure optimum operation. The SCD is no substitute for efficient water treatment management

Landscape heterogeneity shapes taxonomic diversity of non-breeding birds across fragmented savanna landscapes

There is an ongoing need to integrate agricultural production with wildlife conservation to maintain biodiversity, especially in developing countries. The landscape heterogeneity hypothesis identifies a potential means for promoting biodiversity in agricultural landscapes by emphasizing that increasing heterogeneity can increase biodiversity. However, the importance of landscape heterogeneity relative to habitat amount and vegetation structure is poorly understood, particularly regarding the relative importance of different components of landscape heterogeneity. We investigated how taxonomic, functional, and phylogenetic diversity of non-breeding birds responded to two components of landscape heterogeneity, compositional and configurational heterogeneity, and compared the importance of the landscape heterogeneity hypothesis relative to the habitat amount hypothesis and vegetation structural heterogeneity hypothesis. To do so, we conducted point counts at 80 plots across 16 landscapes during June–July 2016 in northeastern Swaziland, a sub-tropical savanna. We found a positive effect of landscape heterogeneity on taxonomic diversity, but no effect of habitat amount or vegetation structure. In contrast to taxonomic diversity, we found a positive trend between the amount of savanna habitat and phylogenetic diversity. In agricultural mosaics in subtropical savannas, conservation value may be created if landscape compositional heterogeneity, landscape configurational heterogeneity, and large areas of habitat are incorporated into land planning. Our findings show that it is important to use multiple measures of diversity in conjunction with various landscape and habitat measures when designing conservation management strategies.A National Science Foundation ISE Grant (No. 1459882 to RAM, AM, and RJF) and the College of Agriculture and Life Science at the University of Florida and the USDA National Institute of Food and Agriculture.http://link.springer.com/journal/105312019-08-01hj2018Mammal Research InstituteZoology and Entomolog

Influence of sugarcane growth stages on bird diversity and community structure in an agricultural-savanna environment

Agricultural intensification is a threat to terrestrial ecosystems around the world. Agricultural areas, especially monocultures, create homogenous landscapes for wildlife. However, certain crops, such as sugarcane, are harvested in phases, creating a mosaic of fields in different stages of growth. We investigated changes in avian communities across four different sugarcane growth stages: emerging, short, medium and tall sugarcane, as well as control sites that represented native savanna habitat in northeast Eswatini prior to conversion to agriculture. In total, we sampled nine sites in sugarcane fields (at different growth stages) and three in native savanna. We conducted bird counts at 5-week intervals along 200m line transects over both the breeding and non-breeding seasons. We recorded a total of 124 bird species belonging to 58 families. Bird species richness and diversity were higher in savannas compared to any stages of growth in sugarcane. In contrast, functional beta diversity and uniqueness were higher in sugarcane than in savanna. Community composition was also different between the two land-uses. While there was overlap in bird species composition between different sugarcane growth stages, there was high beta diversity and high turnover between sites, indicative of the high temporal and spatial variability in bird communities in sugarcane fields. We demonstrated that the spatial and temporal variability created by the different growth stages of sugarcane promotes the occurrence of species with different traits, which may contribute to ecosystem functioning and promote the conservation of bird species as sugarcane fields can provide resource complementation for species with different needs.http://www.cell.com/heliyonam2022Mammal Research InstituteZoology and Entomolog

Using species distribution models to gauge the completeness of the bat checklist of Eswatini

National species checklists are important for a variety of reasons, including biodiversity conservation. However, these national checklists are rarely complete, and it is not easy to gauge how many species have been overlooked or what the taxonomic identities of overlooked species would be. This is particularly the case for small, elusive, or nocturnal species such as bats. Despite their diversity and importance as ecosystem service providers, bat distributions are poorly known throughout much of Africa. We present a national checklist of bats for a small African country, Eswatini, by compiling species from museum specimens and literature records. A total of 32 species of bats have been recorded from the country. Since 1995, new species have continued to be recorded in Eswatini, with five additional species added since the last published checklist in 2016, suggesting that some species may still be overlooked. In order to determine what species these may be, we used species distribution models based on the occurrence records of bats from southern Africa to predict what species would occur in Eswatini, which was then compared with what has been collected and deposited in museums. Our models predicted that a total of 47 species are likely to occur in Eswatini compared with 32 species collected to date. Our data suggest that the national checklist of bats of Eswatini is not yet complete and that further species are expected to be recorded for the country. We suggest that species distribution models can be useful for gauging the completeness of national checklists and predicting which species may have been overlooked.The National Science Foundation Graduate Research Fellowship, a Student Research Grant from Bat Conservation International, a National Geographic Young Explorer’s Grant 9635-14, and The Explorers Club Exploration Fund – Mamont Scholars Program.http://link.springer.com/journal/103442022-01-26hj2021Mammal Research InstituteZoology and Entomolog