The purpose of this thesis is to understand and analyse the issues of grey water generation and disposal in peri-urban areas of Dar es Salaam in Tanzania and to propose a suitable solution to which includes designing a treatment system for grey water (water from shower, washing and kitchen). The purification will eliminate the sanitation issues that are brought by exposing untreated grey water to the environment as well save freshwater. This will be implemented with regard to local conditions in Dar es Salaam, Tanzania. Water-borne and vector-borne diseases are mainly brought by untreated grey water, which sadly enough causes thousands of death cases every year in Tanzania. The year between 2004- 2005, 154551 cases of dysentery were reported with 170 deaths. It was also reported, 863488 cases of typhoid with 1167 deaths and last but not least 12923 cases of cholera from with 350 deaths. Deaths that were caused by diarrhoea were also reported, whereby, 90 % of them are children. According to the interviews that were conducted, people would not want to recycle the grey water for example for washing due to socio-cultural context where water is considered dirty even after treatment. They had difficulties in believing that the same dirty grey water can be purified and reused again for various domestic activities. The conducted characterisation of grey water showed the tested grey water has relatively high levels of BOD, basic pH, higher than average values of TSS, relatively low levels of DO, increased salinity and average level of FC. The analyses were performed on the most polluted grey water from every source. The volume of household produced grey water varies strongly, depending on socio-economic situation of the household and type of access to water supply. From estimation, the volume varies approximately between 60 -160 l/day and household for a low income household. Living wall was proposed as grey water treatment system, because of its suitability to the peri-urban settlement and tropical climate. The system consists of concrete boxes placed over each other, filled with inner porous material and planted with plants. The system purifies grey water as it percolates through it and at the same time provides a vertical space for growing plants. The plants for the treatment system were chosen to Typha latifolia and Scirpus species. The plants are growing in Tanzania and are being used for wastewater treatment purposes. The plants are tolerant to increased salinity and can grow in alkaline soil. The cleaning effectiveness of the system was not tested, but only roughly estimated with help of values from a similar treatment system build in Gotland, Sweden. Hence, the reuse of grey water in this geographical location suits best for irrigation in rural and peri-urban areas with potential for agriculture as well as groundwater recharge in the peri-urban and urban areas. Recharging groundwater with treated grey water has a potential to be observed as an indirect and long term reuse of the water as it reconnects in the hydrological cycle.

<p>The purpose of this thesis is to understand and analyse the issues of grey water generation and disposal in peri-urban areas of Dar es Salaam in Tanzania and to propose a suitable solution to which includes designing a treatment system for grey water (water from shower, washing and kitchen). The purification will eliminate the sanitation issues that are brought by exposing untreated grey water to the environment as well save freshwater. This will be implemented with regard to local conditions in Dar es Salaam, Tanzania.</p><p>Water-borne and vector-borne diseases are mainly brought by untreated grey water, which sadly enough causes thousands of death cases every year in Tanzania. The year between 2004- 2005, 154551 cases of dysentery were reported with 170 deaths. It was also reported, 863488 cases of typhoid with 1167 deaths and last but not least 12923 cases of cholera from with 350 deaths. Deaths that were caused by diarrhoea were also reported, whereby, 90 % of them are children.</p><p>According to the interviews that were conducted, people would not want to recycle the grey water for example for washing due to socio-cultural context where water is considered dirty even after treatment. They had difficulties in believing that the same dirty grey water can be purified and reused again for various domestic activities.</p><p>The conducted characterisation of grey water showed the tested grey water has relatively high levels of BOD, basic pH, higher than average values of TSS, relatively low levels of DO, increased salinity and average level of FC. The analyses were performed on the most polluted grey water from every source. The volume of household produced grey water varies strongly, depending on socio-economic situation of the household and type of access to water supply. From estimation, the volume varies approximately between 60 -160 l/day and household for a low income household.</p><p>Living wall was proposed as grey water treatment system, because of its suitability to the peri-urban settlement and tropical climate. The system consists of concrete boxes placed over each other, filled with inner porous material and planted with plants. The system purifies grey water as it percolates through it and at the same time provides a vertical space for growing plants.</p><p>The plants for the treatment system were chosen to Typha latifolia and Scirpus species. The plants are growing in Tanzania and are being used for wastewater treatment purposes. The plants are tolerant to increased salinity and can grow in alkaline soil.</p><p>The cleaning effectiveness of the system was not tested, but only roughly estimated with help of values from a similar treatment system build in Gotland, Sweden.</p><p>Hence, the reuse of grey water in this geographical location suits best for irrigation in rural and peri-urban areas with potential for agriculture as well as groundwater recharge in the peri-urban and urban areas. Recharging groundwater with treated grey water has a potential to be observed as an indirect and long term reuse of the water as it reconnects in the hydrological cycle.</p>

Grey water is sewage water from bath, bathtub, sinks, washing machines and washers. This water can be cleaned to white water usefull for irrigation, flashing toilets, cleaning cars and for cleaning. This master´s thesis deals with management of water and their possibilities. First part contains description about possibilities of saving drinking water and their the most effective saving. Next part consists study of technological link for grey water cleaning and calculation of saving water with rate of return.

This study focused on the investigation of the impact of household cleaning and personal care products on the quality of grey water and the assessment and optimisation of grey water treatment by a novel constructed wetland design. The prototype wetland design which comprised three-stage cascading beds (0.27 m 2 by 0.20 m deep) with sand media, (d10: 1.0 mm and d90: 4.0 mm) was tested for treatment performance to meet non-potable reuse standards in three versions, unplanted open beds, unplanted covered beds, and planted beds (comprising mixtures of Iris pseudacorus, Iris chrysographes, Carex elata Aurea and Mentha aquatica). The prototypes were benchmarked against a standard single-pass wetland (6 m 2 by 0.7 m) planted with Phragmites australis. Performance was measured in terms of removal of conventional water quality determinant parameters, as well as Total coliforms and E coli, and surfactants. Microbial dynamics were also monitored during the study by looking at variations in microbial compositions with time for the different wetlands. All the wetland versions effectively removed more than 98 % turbidity and organics meeting the most stringent reuse wastewater reuse standards of < 2.0 NTU and < 10 mg BOD5/L respectively. The influent grey water had low BOD:COD ratio ranging from 0.27 – 0.45, which is indicative of low biodegradability. The comparison of the cascade wetland performances showed the following: open beds > planted = covered, with the open beds version meeting reuse standards virtually throughout the monitoring period, despite recurrence of schmutsdecke in the top bed. All wetland technologies supported viable populations of microorganisms. Only phospholipid fatty acids (PLFAs) of lower carbon chain length (< C20) had concentrations greater than 1 mol %, in all the wetlands beds, confirming that the majority of the PLFAs in the media were from contribution of microbial organisms and not plant organic matter. Characterisation of microbial organisms was carried out to understand the constructed wetlands functioning and thus the treatment processes. The household products showed nutrient deficiency signifying low treatability. Product branding did not show correlation with any water quality parameters. In terms of toxicity, laundry and cleaning products were more inhibiting to soil microorganisms than were personal care products.

Water is a prerequisite for life on our planet. Due to climate change and pollution, water availability for agricultural production, industry and households is increasingly put at risk. With agriculture being the largest water user as well as polluter worldwide, we estimate anthropogenic nitrogen and phosphorus emissions to fresh water related to global crop production at a spatial resolution level of 5 by 5 arc min and calculate the grey water footprints (GWF) related to EU-27's crop production. A multiregional input-output model is used to trace the the GWF embodied in the final consumption of crop products by the EU-27. The total GWF related to crop production in the EU-27 in 2007 was 1 × 1012 m3/year. Spain contributed about 40% to this total. Production of cereals (wheat, rice and other cereals) take the largest share, accounting for 30% of the GWF, followed by fruits (17%), vegetables (14%), and oil crops (13%). The total agricultural GWF of the EU-27 related to crop consumption was 1830 billion m3/year, which is 3700 m3/year per capita on average. Overall, the EU-27 was able to externalize about 41% of the GWF to the rest of the world through imports of crop products.

Grey water reuse has attracted more and more attention among researchers and professionals in recent years. As most of the Chinese cities are undergoing the process of fast urbanization and economic development, many water-related problems have occurred and urban water resources management has become a strategic issue. The urge to reconsider the conventional ways of utilizing water and discharging the wastewater in cities is calling. As a relatively simple and flexible way, decentralized grey water reuse system can help to make the first step in achieving a sustainable urban water management. However, whether it is feasible in China is still a question. This paper aims at looking for the answer based on a survey and interviews with professionals in the fields from different Chinese cities. The result shows “reuse” as one of the solutions of solving water shortage and achieving sustainable water management is not as simple as one may think. In general, decentralized urban grey water / wastewater reuse is not easy to flourish in China in the near future though most of the respondents hold a positive attitude about reuse itself. To explain this difference between attitude and actual planning we need more historical, political and social-economic understanding with a touch of “Chinese characteristics”.

Då klimatförändringarna runt om i världen accelererar med torka så behöver man under regnperioder ta tillvara på dag- och gråvatten istället för att släppa ut det i dagvattensystemet. I Örebro, Sverige, finns en byggnad vid namn Citypassagen, som använder sig av ett system som spolar toaletter med uppsamlat regnvatten. Att spara dagvatten och använda som spolvatten är en smart lösning på vattenbrist, det kan dock föra in risker in i byggnaden som skulle kunna smitta människor som befinner sig vid och använder toaletterna. Detta tillsammans med riskerna vid gråvattenanvändning undersöks närmare i den här rapporten, samt att det undersöks om implementering av ett sådant system som använder dag- och gråvattnet för toalettspolning kan vara energieffektivt.Rapporten kommer fram till att det främst är bakterier och patogener som skulle kunna orsaka smitta hos människor vid användning av dessa dag- och gråvattenspolande toaletter, då de kan förekomma som aerosoler medan de andra undersökta områdena inte kan förekomma som aerosoler. Det fastställs även att energibesparing kan göras med ett spolvattensystem som använder sig av regnvatten då reningen inte kommer att bli lika omfattande som vid ett traditionellt reningsverk. Slutsatsen är att risker som legionella pneumophila kan smitta som aerosoler. Andra smittorisker är E-coli, Cryptosporidium och Giardia, patogener som kan återfinnas i gråvatten. Energibesparingar kan främst göras vid reningsprocessen, då samma rigorösa reningsprocess som återfinns i reningsverk inte krävs. / With accelerating climate change bringing droughts around the world, the necessity to use urban runoff and grey water as a resource grows. In Örebro, Sweden, there is a building called Citypassagen, which uses a system of collected rainwater for flushing of toilets. To use urban runoff for toilet flushing is a smart solution to shortage of water availability, though it can also mean the exposure of health risks to people who use the toilets. These risks, accompanied by the risks of grey water usage, are examined in this report, and also if the implementation of a system that uses urban runoff and grey water for toilet flushing can be viewed as a means to energy savings.This report finds that bacteria and pathogens are the primary source of potential infection when using urban runoff or grey water flushing toilets, because of their ability to occur as aerosols, unlike the other examined risks. It is also established that energy savings can be made with a flushing system that uses rainwater, because the purification process is not as extensive compared to the process used in a traditional treatment plant. The conclusion is that risks such as legionella pneumophila can infect as an aerosol. Other risks of infection are E-coli, Cryptosporidium and Giardia, pathogens that can be traced in grey water. Energy savings can primarily be achieved in the purification process, because the same rigorous process used in traditional treatment plants is not necessary.

Stora mängder energi lämnar bostäder med avloppsvattnet utan något bemödande att återföra det uppvärmda vattnets värmeenergi tillbaka till byggnaden. Med ökade klimatskalsförbättringar av traditionellt slag för att möta de nära-nollenergikrav på nybyggnationer för bostadshus som träder i kraft i slutet av 2020 kan energiförlusterna i byggnader till allt större del allokeras till det avloppsvatten som lämnar byggnaden. Målet med detta arbete är att undersöka huruvida betydande energibesparingar inom området kan erhållas, samt att bedöma de ekonomiska möjligheterna och utsikterna för att tillvarata värmeenergi med hjälp av värmepump ur gråvatten från  flerbostadshus uppkopplade mot fjärrvärmenät. Och i och med det visa vilka faktorer som visar sig utöva påverkan på de driftmässiga besparingsmöjligheterna samt uppvisa hur pass känsligt resultatet är i förhållande till ett urval av dessa faktorer. Arbetet utgörs av och har genomförts i två delar: en litteraturstudie och en beräkningsstudie. Avloppsvatten kan delas in i spillvatten, dagvatten och dräneringsvatten. Spillvatten är avfallsbidraget från hushåll och andra fastigheter till avloppet. Hushållens spillvatten kan i sin tur indelas i gråvatten och svartvatten. Gråvatten är det vatten som kommer från bad, disk och tvätt, vilket av det skälet även kallas BDT-vatten. Svartvatten är det vatten som spolas ut från toaletter, och kallas därför även klosettvatten. Vid separerade flöden infinner sig möjligheten att tillvarata värmeenergi direkt från gråvatten, som också är den varmare, volymmässigt största och mer lätthanterliga fraktionen, både ur vattenrenings- och värmeåtervinningssynpunkt. Studier på källsorterande system visar på flera fördelar i stort med att hålla hushållens avloppsflöde separerade, såsom bland annat utökad resurseffektivitet av kväve och fosfor vid reningsverken. Nedsmutsning av värmeväxlarytor, i synnerhet av biofilm, utgör en utmaning då avloppsvatten ska användas som värmekälla och är något som måste beaktas även vid tillvaratagande av värme ur gråvatten. Resultatet från beräkningsstudien av ett enskilt fall med tappvarmvattenförvärmning, givet en rad antaganden, gav en driftmässig kostnadsbesparing på cirka 31 000 kr per år och ett nuvärde på dessa årliga besparingar sett över 20 år på cirka 355 000 kr. Energibesparingen uppgick till cirka 63 000 kWh per år vilket innebär en minskning av totala behovet av köpt energi för tappvarmvattenproduktion med cirka 67 % vid uppvärmning av tappvarmvatten till 55 °C. Känslighetsanalysen visar att avgörande parametrar i beräkningsstudien såsom el- och fjärrvärmepris, värmepumpens livslängd och kalkylräntan medför relativt stora förändringar av resultatet om de tillåts att variera. Det är uppenbart att det finns stora mängder energi att återvinna, det är också uppenbart att svårigheter gör att gråvatten som värmekälla inte kan behandlas lättvindigt då bland annat den långsiktiga utvecklingen av vattenanvändningen och hög föroreningsgrad är faktorer som måste beaktas i tillägg till de faktorer som tas upp i känslighetsanalysen. Dubbla system med fjärrvärme och värmepump innebär en högre investering men är samtidigt något som kan ses som ett verktyg för att utnyttja de ökande energiprisvariationer som en allt större andel förnybar icke-reglerbar elproduktion sannolikt innebär genom att helt enkelt kunna variera uppvärmningssätt efter varierande energipriser och finna optimal andelsfördelning. För en fastighetsägare blir det i takt med en sådan utveckling alltmer gynnsamt att kunna välja det som för tiden är det billigaste alternativet. / Large amounts of energy leave homes with wastewater without any effort to return the heated water's thermal energy back to the building. With increased thermal envelope improvements of a traditional nature to meet the nearly zero-energy requirements for residential buildings that will come into effect by the end of 2020, energy losses in buildings can increasingly be allocated to the wastewater leaving the building. The aim of this work is to investigate whether significant energy savings in the mentioned area can be obtained, as well as to assess the economic opportunities and prospects for utilizing heat energy from grey water from multi-residential buildings connected to district heating networks with the help of a heat pump. And by that show which factors are shown to influence the operational savings and how sensitive the results are in relation to a selection of these factors. The work consists of and has been carried out in two parts: a literature study and a calculation study. Household wastewater can be divided into grey and black water. Grey water is the water that comes from bath, dishes and laundry and black water is the water that is flushed out of the toilets. Separated flows reveal the possibility of utilizing thermal energy directly from grey water, which is also the warmer, volume largest and more manageable fraction, both from a water purification and heat recovery standpoint. Studies on source separated systems show a wide range of benefits, largely by keeping household wastewater separated, such as increased resource efficiency of nitrogen and phosphorus at the wastewater treatment plants. The contamination of heat exchanger surfaces, especially biofilm, poses a challenge when wastewater is used as a heat source and is something that has to be taken into account even when using grey water as a heat source. The result of the calculations of an individual case with preheating of domestic hot water, given a series of assumptions, resulted in operational cost savings of approximately SEK 31,000 per year and a present value of these annual savings over 20 years of approximately SEK 355,000. Energy savings amounted to approximately 63,000 kWh per year, which means a reduction of the total need for purchased energy for domestic hot water production by 67 % with an assumption of a final domestic hot water temperature of 55 °C. The sensitivity analysis shows that crucial parameters in the calculation study such as electrical and district heating price, heat pump life and discount rate entail relatively large changes in profit if allowed to vary. It is obvious that there are large amounts of energy to potentially recycle. It is also obvious that difficulties cause grey water as a source of heat not be treated easily because, among other things, the long-term development of household water use and high pollution rates are factors that must be considered in addition to the factors brought up in the sensitivity analysis. District heating and heat pump combined imply a higher investment than a single heating system, but at the same time is something that can be seen as a tool for utilizing the assumed increasing energy price variations that an increasing proportion of intermittent renewable power generation implies simply by varying heating configuration with changes in energy prices and finding the optimal share. For a property owner, it would at this point be favorable to be able to choose what the cheapest option is currently.

Developing nations face insurmountable challenges to reliably and sustainably provide energy and water to the population. These resources are intricately entwined such that decisions on the use of one affects the other (energy-water nexus). Inadequate and ageing infrastructure, increased population and connectivity, urbanization, improved standards of living and spatially uneven rainfall are some of the reasons causing this insecurity. Expanding and developing new supply infrastructure is not sustainable due to sky high costs and negative environmental impact such as increased greenhouse gas emissions and over extraction of surface water. The exponentially increasing demand, way above the capacity of supply infrastructure in most developing countries, requires urgent mitigation strategies through demand side management (DSM). The DSM strategies seek to increase efficiency of use of available resources and reducing demand from utilities in the short, medium and long term. Renewable energy, rooftop rain water harvesting, pump-storage scheme and grey water recycling are some alternatives being used to curb the insecurity. However, renewable energy and rooftop water harvesting are spasmodic in nature hampering their adoption as the sole supply options for energy and water respectively. The built environment is one of the largest energy and water consuming sectors in the world presenting a huge potential towards conserving and increasing efficiency of these resources. For this reason, coupled with the 1970s energy challenges, the concept of green buildings seeking to, among other factors, reduce the consumption of energy and water sprung up. Conventionally, policy makers, industry players and researchers have made decisions on either resource independently, with little knowledge on the effect it would have on the other. It is therefore imperative that optimal integration of alternative sources and resource efficient technologies are implemented and analysed jointly in order to achieve maximum benefits. This is a step closer to achieving green buildings while also improving energy and water security. A multifaceted approach to save energy and water should integrate appropriate resource efficient technology, alternative source and an advanced and reliable control system to coordinate their operation. In a typical South African urban residential house, water heating is one of the most energy and water intensive end uses while lawn irrigation is the highest water intensive end use occasioned by low rainfall and high evaporation. Therefore, seamless integration of these alternative supply and most resource intensive end uses provides the highest potential towards resource conservation. This thesis introduces the first practical and economical attempt to integrate various alternative energy and water supply options with efficient devices. The multifaceted approach used in this research has proven that optimal control strategy can significantly reduce the cost of these resources, bring in revenue through renewable energy sales, reuse waste water and reduce the demand for grid energy, water and waste water services. This thesis is generally divided into cold and hot water categories; both of which energy-water nexus DSM is carried out. Open-loop optimal and closed-loop model predictive (MPC) control strategies that minimize the objective while meeting present technical and operational constraints are designed. In cold water systems, open-loop optimal and MPC strategies are designed to improve water reliability through a pump storage system. Energy efficiency (EE) of the pump is achieved through optimally shifting the load to off-peak period of the time-of-use (TOU) tariff in South Africa. Thereafter, an open-loop optimal control strategy is developed for rooftop rain water harvesting for lawn irrigation. The controller ensures water is conserved by using the stored rain water and ensuring only the required amount of water is used for irrigation. Further, EE is achieved through load shifting of the pump subject to the TOU tariff. The two control strategies are then developed to operate a grey water recycling system that is useful in meeting non-potable water demand such as toilet flushing and lawn irrigation and EE is achieved through shifting of pump's load. Finally, the two control strategies are designed for an integrated rain and grey water recycling for a residential house, whose life cycle cost (LCC) analysis is carried out. The hot water category is more energy intensive, and therefore, the open-loop optimal control strategy is developed to control a heat pump water heater (HPWH) and an instantaneous shower, both powered by grid-tied renewable energy systems. Solar and wind energy are used due to their abundance in South Africa. Thereafter, the MPC strategy is developed to power same devices with renewable energy systems. In both strategies, energy is saved through the use of renewable energy sources, that also bring in revenue through sale of excess power back to the grid. In addition, water is conserved through heating the cold water in the pipes using the instantaneous shower rather than running it down the drain while waiting for hot water to arrive. LCC analysis is also carried out for this strategy. Each of the two control strategies has its strengths. The open loop optimal control is easier and cheaper to implement but is only suitable in cases where uncertainties and disturbances affecting the system do not alter the demand pattern for water in a major way. Conversely, the closed-loop MPC strategy is more complicated and costly to implement due to additional components like sensors, but comes with great robustness against uncertainties and disturbances. Both strategies are beneficial in ensuring security and reliability of energy and water is achieved. Importantly, technology alone cannot have sustainable DSM impact. Public education and awareness on importance of energy and water savings, improved efficiency and effect on supply infrastructure and greenhouse gas emissions are essential. Awareness is also important in enabling the acceptance of these technological advancements by the society. / Thesis (PhD)--University of Pretoria, 2017. / National Hub for Energy Efficiency and Demand Side Management (EEDSM) / University of Pretoria / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The objective of this research was to obtain clean drinkable water from treated sewage effluent by using a solar-powered distillation cycle. Technologies and concepts were borrowed from the solar desalination industry to propose a unique circular distillation cell design. From the design, a specific mathematical correlation was developed to predict the distillate mass flow rate by using only evaporation and condensation temperature as inputs. This model was incorporated into a simulation model built using Transient System Simulation software. Long-term simulations were carried out to determine the operating capabilities of the design. A prototype was successfully constructed and operated. Experimental results indicated good agreement with the mass flow rate mathematical correlation. Water quality levels were tested against the South African National Standard 241 national drinking water quality standard. Four quality parameters are outside acceptable levels. Evidence suggested that acceptable quality levels could be reached. The circular distillation cell design is a major contribution made by this research. Another contribution is the simulation model capable of predicting an output for different locations. Finally, the proposed prototype is potentially a very valuable device contributing towards the reduction of consumer demand in terms of water and energy as well as the household load on the wastewater treatment system. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om te beskryf hoe behandelde rioolwater deur middel van ’n son aangedrewe distillasiesisteem gesuiwer kan word om drinkbare water as eindproduk te lewer. Die nodige tegnologieë en konsepte is oorgeneem uit kommersiële sonaangedrewe ontsoutingsisteme om met ’n unieke ontwerp voorendag te kom wat uit ’n sirkelvormige natuurlike konveksie distillasiesel bestaan. Met behulp van hierdie ontwerp is ’n wiskundige korrelasie ontwikkel om die gesuiwerde water se massavloei te bepaal. Slegs die verdampings- en kondensasietemperature word as insetwaardes gebruik om die massavloei te bereken. ’n Simulasiemodel is met behulp van die Transient System Simulation programmatuur gebou. Die wiskundige korrelasie is by die simulasiemodel geïnkorporeer om langtermynsimulasies te kan uitvoer. Voorts is ’n demonstrasiemodel suksesvol gebou en aangedryf. Eksperimentele resultate toon goeie ooreenstemming met die simulasieresultate. Die gesuiwerde water se gehalte is met die nationale SANS 241 drinkwaterstandaard as maatstaf getoets. Slegs vier gehalteparameters val buite die aanvaarbare vlakke, hoewel dit blyk dat hierdie elemente wel tot aanvaarbare vlakke verlaag kan word. Hierdie navorsing se grootstet bydrae is die ontwerp van die unieke sirkelvormige distillasiesel. ’n Bykomende bydra is die aanpasbaarheid van die simulasiemodel sodat dit produksievermoë op verskillende plekke kan voorspel. Die demonstrasiemodel is ’n potensieel waardevolle ontwerp wat kan bydra tot die verlaging in verbruikersaanvraag na water en energie. ’n Ontwerp van hierdie aard kan die las wat huishoudings op suiweringaanlegte vir rioolwater plaas, verlig.