Greywater Rainwater Treatment System
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Combined greywater-rainwater treatment system can minimize the potable water usage in toilet flushing by reusing treated water from bathroom and laundry. However, combined system is not widely used due to risk associated with water quality and relatively higher cost compared to financial benefit even though environmental benefit of using recycled water is agreed. This project aims to investigate different greywater and rainwater treatment systems to quantify potential water availability and conduct cost benefit analysis of different combined systems. Different water consumption data will be collected from Central Highland Water Ballarat. Daily rainfall data from Bureau of Meteorology Victoria will be used to design storage tank capacity. Analysis will be performed on different water treatment systems to determine the costs and benefits of using the system. The focus will be to use treated graywater first and rainwater in the combined treatment system will be used as a supplementary source. One of the main outcomes of the project would be to evaluate system cost and energy cost to identify the structure that would make the system economically viable.
Table of Contents
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Australia has been experiencing the rapid population boom since many decades. Due to population growth, water demand is increasing continuously in urban areas of Australia. According to Australian Bureau of Statistics, the state of Victoria has highest population growth of 2.3% in year 2016-17 and in 2016, the population of Ballarat was 157,485 and it is rapidly increasing continuously every year (Australian Bureau of Statistics, 2017). It has been a challenging job for the government to fulfill the water demand for the growing population and there is a need to develop strong and effective strategy to save and manage water and its resources. Advancement and utilization of such water sources are very costly and may harm to the environment. More consumption of water implies more production of wastewater. The best option to reduce the water demand is to store and reuse rainwater and graywater for different purposes by applying proper treatment.
Fresh drinkable water has been used for toilet flushing. The use of domestic rainwater and greywater treatment plants reduces public water supply demand significantly. Some ordinary rainwater tanks have been used to store rainwater and reuse it in gardening and toilet flushing. Only greywater tanks may not enough to fulfil the requirement of toilet flushing. Addition of treated rainwater with greywater increases the amount of reusable water.
To increase treated graywater, different treatment methods have been devised and this project is intended to investigate on such existing systems such as granular activated carbon filters (GAC), multimedia filter (MMF), ozone disinfectant, and sedimentation. The study will analyze these systems that utilize the rain water and treated greywater for toilet flushing and identifies different socio-economic factors such as demography, cost, preferences, and seasonal variations that affects them. It is also going to determine the quantity of fresh water that can be saved by implementing these systems. Also, it will help to study the quality of treated water. It would recommend the best system for the intended purpose with efficiency within social economics and environmental domains in Ballarat Region.
The scope of this project is to quantify the volume of water from daily rainfall patterns and treated graywater to design the combined water tank that can be used for toilet flushing and suggest the best method to disinfect graywater and make is reusable.
In Ballarat region, very few houses have installed rainwater and greywater tanks. An installation cost of this systems may higher and people neglecting its long-term economic benefits. Combined system of rainwater tank with septic tank will provide higher amount of water for toilet flushing. By analyzing rainfall pattern in Ballarat region helps to find design volume of water required to design of rainwater tank. Also, investigating different systems to disinfect greywater will helps to find best suitable treatment process that can combined with rainwater tank to reuse maximum amount of water for toilet flushing.
1.1 Aim and Objectives
The aim of this project is to propose a combined system for reusing graywater and rainwater for toilet flushing in Ballarat region.
The main objectives of this project include,
- Quantifying the usable amount of graywater produced from bathroom and laundry.
- Quantifying the usable rainwater volume from daily rainfall pattern.
- Analyze different options that can be combined with greywater and rainwater treatment systems for toilet flushing.
- Conduct cost-benefit analysis of the combined system for different tariff and energy cost.
- Hybrid rainwater-greywater system
- Potable water saving
- Activated carbon filters
- Cost-Benefit Analysis
- Energy intensity
1.3 Benefits and Stakeholders
Residents, the city council of Ballarat, Local Governing bodies and companies that produce the equipment for the treated greywater and rainwater reusing systems are the stakeholders.
2.0 Literature Review
The review on hybrid rainwater-greywater system by Janet, et al. (2017) on hybrid rainwater-greywater system shows that evaluated domestic rainwater system provides more than 90% of reusable water for toilet flushing, laundry, and irrigation purposes. According to New South wales government, (1998), water supply in rural areas of Australia are consented to be low as 100 l/p/d in the areas without arranged water supply.
2.1 Greywater Quality:
Combined rainwater-greywater mixture treatment requires chemical processes to remove solids, organics, and surfactants whereas aerobic biological treatment processes required for removal of organic particles with high organic strength (Janet, et al. 2017). There are different methods to treat greywater which are available in this modern era. Multimedia filter (MMF), a granular activated carbon filter (GAC), and ozone disinfection treatment were studies in assessment of greywater quality and performance of pilot-scaled decentralized hybrid treatment system by Janet, et al. (2017) and it was found that granular activated carbon filter (GAC) was the most effectual treatment method of removing COD, turbidity, color, and zinc.
According to Ramiro and Jan, (2015) health risk assessment discloses that in greywater, nearly 280 organic micro-pollutants have been recognized. Environmental quality standards (EQS) were established by European Water Framework Directive (WFD) which shows that 41 dangerous chemical substance found in greywater are potentially hazardous for health must be treated before reusing it. Study by Adi and Amit (2018) on greywater shows that greywater reuse poses health risks due to presence of pathogenic microorganisms and it also causes environmental risks due to sodium, pH and surfactants.
Study on greywater quality done by O`Toole et al. (2012) shows that presence of pathogenic E. coli in the greywater can cause serious human dieses. Study on opportunistic pathogens done by Hamilton, et al. (2016) shows that pathogens found in rainwater such as Legionella spp., Mycobacterium avium complex (MAC), and Pseudomonas aeruginosa causes illness primarily to children, and/or elders, and those with weakened immune systems.
2.2 Rainwater Harvesting:
In urban water planning, ‘Plugrisost’ is the best model simulation tool in design stage of sizing of storage tank, estimated cost, and quantitative environmental analysis (Tito, et al. 2015). It also provides economic information about rainwater tank sizing and estimates. A case study by Monzur, et al. (2011) shows that roof area is directly affects the storage capacity. For larger roof area, high volume water storage tanks are required to achieve maximum efficiency, proper analysis and design before construction. Rainwater harvesting system (RHS) consume three times more energy than conventional town water supply system. In rainwater harvesting system, high intensity energy required in pump startup and standby mode (Abel, et al. 2014).
Reliability analysis of rainwater tank has been done by Monzur, et al. (2012) in which, it is found that for smaller roof size, it cannot attain 100% reliability. With larger roof areas, reliability increase with increase in tank storage capacity. In treatment of rainwater, some low-cost systems that can be used are disinfection, slow sand filtration, and pasteurisation (Zhe, et al. 2010).
2.3 Combined Greywater-Rainwater System
Research on economic analysis to evaluate the benefits of rainwater and greywater reuse describes that potable water saving by combined reuse of rainwater and greywater is higher than use them separately (Ghisi, et al., 2007). Study by Janet, et al. (2017) shows that decentralized hybrid rainwater-greywater system can be used as independent greywater during dry season and rainwater during rainy season resulting higher amount of water saving. Analysis of a pilot-scale decentralized hybrid rainwater-greywater system shows that pollutant removal efficiency of this system is higher at 10L/min of hydraulic loading rate than 20L/min, as filter absorbs more pollutants with higher retention time (Janet, et al. 2017).
2.4 Cost of Treatment system
Studies done by Caleb, et al. (2018) shows that to make rainwater harvesting system more economically viable, it is recommended to reduce installation costs of pumps and plumbing system instead of changing water price. Results shows that the capital cost which has highest contribution to the treatment system which includes, maintenance, operation and replacement costs (Thulo & Sharma. 2014). A net benefit value (NBV) model has been derived by Chen and Wang (2009) to evaluate cost-benefit in which the larger NBV value, the more beneficial treatment system.
The analysis done by Zita, et al. (2015) suggests that treatment system with high installation cost and maintenance cost may be economically feasible for large number of residential units. In addition, electricity and chemicals depending on treatment technology are included in operational costs. According to Caleb, et al. (2018), larger size of storage tank is better to get maximum benefits from treatment system. Also, this study shows that increasing number of users results into improved economic viability of rainwater harvesting system.
The overall methodology is described in following steps,
- Select a location, Ballarat which is in the state of Victoria having annual rainfall intensity below national average rainfall.
- Collect water consumption data of Ballarat from annual water report of regional water corporation Central Highlands Water providing fresh drinkable water in Ballarat and surrounding regions. Collect daily rainfall data of Ballarat from 2008 to 2017.
- Quantify the amount of water consumed by a person and required water quantity for different household activities such as, bathroom, laundry, and toilets.
- Quantify the amount of water collected by rainfall and design volume of rainwater tank required for its storage.
- Analysis of greywater and rainwater treatment systems based on literatures and reports to get desired quality of water according to Australian standards.
- Analyze the combined greywater and rainwater treatment system to reuse in toilet flushing.
- Conduct cost-benefit analysis of the combined system for different tariff and energy cost
- Risk Assessment of combined greywater-rainwater treatment system.
3.1 Data collection:
From annual reports of Central Highlands Water, daily residential potable water consumption will be accessed. Quantity of water consumed in bathroom, laundry, and toilets will be calculated.
From Australian Bureau of Meteorology, daily rainfall data in mm will be collected from 2008 to 2017. These data will be used to calculate design volume of rainwater tank. Ballarat Aerodrome site has been selected to collect daily rainfall intensity for 10 years of period.
3.2 Quantification of water:
Firstly, greywater produced from bathroom and laundry will be collected. Water required for toilet flushing will be quantified. Secondly, monthly average rainfall for each year in mm will be calculated from daily rainfall data collection.
According to HB 230-2008 (Rainwater Tank Design and Installation Handbook), these factors will be considered in designing rainwater tank sizing are listed below.
- Rainfall for the region – rainfall data from Australian Bureau of Meteorology.
- Roof catchment size – specific roof area in square meter
- Allotment size – land availability for storage tank
- Water consumption – daily water consumed by a person and household activities
From the daily rainfall data of Ballarat region, following steps will be considered for sizing rainwater tank.
Step-1: Find monthly average rainfall in mm for 10 years based on daily rainfall data.
From above equation, we will get average rainfall data for each month. It will be used to get maximum amount of water required to store in rainwater tank for a month.
Step-2: Find maximum amount of rainfall from calculated monthly average data to consider maximum amount of water quantity required to be stored for a month.
Step-3: Find Total Run-off for monthly average rainfall from below equation,
Where, A = Efficiency
B = Rainfall (mm)
= Losses due to absorption, wetting, and first flush (mm)
Step-4: Select tank size according to Australian standards
Step-5: prepare table for different roof sizes
For different roof areas, required volume of water tank will be different. So, table containing storage tank size with various roof areas will be developed.
3.3 Analysis of Greywater treatment systems:
Produced greywater from bathrooms and laundry will be collected and transferred to the treatment systems through pipe network. Treated greywater will be used as a preliminary source for toilet flushing.
There are four different treatment systems which are, Granular activated carbon filter (GAC), Multimedia filters, Ozone disinfectant, and Sedimentation will be analyzed. This analysis will be done based on literatures and reports. In detail, Granular activated carbon filters are most effective at removing chlorine, particles such as sediments, volatile organic compounds (VOCs), taste and odor from water. Multimedia filters are used to reduce suspended solids (turbidity) such as silt, clay, grit, organic matters, algae and other microorganisms. Ozone disinfectant is effective in destroying in viruses and bacteria. Processing time for this treatment is 10 to 30 minutes which is comparatively less than other treatments. Sedimentation treatment is used to remove suspended solids by gravity.
According to Australian standards AS 1546.4-2016, there are different treatment levels have been defined for their associated end use. To reuse treated greywater for toilet flushing, Level 1 treatment is required. According to Australian Standards, AS 1546.4-2016 “Domestic greywater treatment system”, there are specific performance and effluent compliance criteria for level 1 treatment process of greywater shown in Table 1.
Table 1: Performance and effluent compliance criteria for Level 1 treatment
|BOD (Biological Oxygen Demand)
|Less than 10 mg/L with no greater than 20 mg/L
|TSS (Total suspended solids)
|Less than 10 mg/L with no greater than 20 mg/L
|Less than 2 NTU with no greater than 5 NTU
|E. coli count
|Less than 1cfu/100mL with maximum of 10cfu/100mL
|Residual FAC Concentration
|≥ 0.5 mg/L
|6 to 9
3.4 Analysis of rainwater treatment systems:
Rainwater will be used for toilet flushing as a supplementary source with greywater. Rainwater will be collected and stored into separate storage tank after treatment. Different pre-storage and post-storage rainwater treatments systems will be analyzed before reusing it.
3.4.1 Pre-storage filtration:
Pre-storage treatment includes minimizing contaminants before storing rainwater into storage tank. Screen mesh, first flush device, pre-storage filter pit will be analyzed to prevent solid contaminants entering storage tank. Pre-storage filtration will be applied with the system before collecting rainwater depending on roof area and usage.
Pre-storage filtration includes, overflow siphons, wet and dry constant filtration, and sediment management. All these systems will be analyzed from different literatures and Australian standards.
3.4.2 Post-storage filtration:
According to Australian Standards HB 230-2008, in rainwater treatment, last stage filtration process will be required to prevent odor and discoloration in the tank before reusing in sanitary flushing.
To achieve maximum requirement of quality as per Australian Standards, pre and post-filtration systems will be analyzed from literatures for all effluent criteria described in Table 1.
3.5 Investigate the combined greywater-rainwater treatment system:
Treated greywater will be used in toilet flushing as a main source and rainwater will be the addition as a supplementary source. So, combined system will provide more reusable water for toilet flushing than individual use.
Investigation will be done by analyzing greywater and rainwater treatment methods and connecting them with pipe network to propose a combined treatment system from different literatures. Different treatment layout will be proposed depending on roof areas, household usage, system cost, and site location.
Below figure describes the proposed schematic diagram of combined greywater-rainwater treatment system.
Figure 1: Schematic diagram of combined greywater-rainwater system
3.6 Cost-Benefit analysis:
Cost-Benefit analysis of combined greywater-rainwater system will be done for economical aspects. In this analysis, different cost of combined treatment system will include installation cost (Ci), maintenance cost (Cm), cost of retrofitting (Cr), and energy cost (Ce).
Here, installation (Ci) cost can be determined by adding total system cost ($), lifetime of system (year) and the volume of water reused after treatment (m3/day). The cost of retrofitting (Cr) includes separate installation and distribution of water plumbing systems required for non-potable water when reusing treated greywater into toilet flushing. The maintenance cost will be taken annually ($/year). Energy cost (Ce) which includes, daily power consumption (kWh/m3) and electricity rate from energy provider ($/kWh).
After installing the treatment system, maintenance of treatment units and pipe network will be required after certain months or years depending on its use. In treatment system, some equipment may also require replacement after certain period then it will directly affect the overall cost of system.
Here, energy cost includes amount of energy required in treatment unit and energy consumed by pump in pipe network. Change in tariff rate of energy or water may affect the overall cost. If tariff rate increases the total cost of system will increase.
Benefits will include cost of greywater quantity saved (Bg), and water quantity saved from corporation supply (Bc).
Cost of greywater quantity saved will be calculated as the tariff rate of treated greywater according to corporation water supply. Cost of water quantity saved from corporation supply will include deduction in use of potable water required in toilet.
The cost-benefit analysis tables and charts will be prepared with respect to different combination of treatment layouts, change in tariff rate of water and energy, initial cost, equipment maintenance and replacement cost. This cost-benefit analysis will help to get economic viability of different combination of systems.
3.7 Risk assessment:
In combined system of greywater and rainwater, these are some possible risks associated as listed below:
Change in tariff rate of energy and water provided by corporation may affect the initial cost of treatment plant. Another possible risk can be clogging in pipe network due to sediments in untreated water before entering treatment units.
3.8 Gantt Chart
3.9 Meeting Attendance Sheet
Investigation on different treatment methods of graywater and use the best option that combines graywater system with redesigned rainwater tank thereby, maximizing the storage of reusable water. Investigation will help to use greywater for toilet flushing with rainwater as a secondary source. Based on cost-benefit analysis, this study will help to create more economically viable system in Ballarat.
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