water utility and involved operations that assesses the system's ability to reduce the risks of different types of threats. The VA exercise identifies weaknesses of our systems security and focuses on the type of possible threats that could keep you for providing a safe and reliable supply of water to the consumers. Once the VA is completed, the water works would know which of its system components might be vulnerable and security upgrades and also the operational changes which will reduce the risks can be identified and prioritized. The exercise would include evaluation of the system, identification of threats and risks, consideration of consequences, evaluation of measures and accordingly action is planned.
2.4 Strategy of Wise Water Management
2.4.1 Greywater Reuses
Society is becoming more water conscious due to shortage, population growth and drought. At the same time, there is concern about the impact and waste of sewage and effluent disposed from sewage treatment plants into our ocean, and other environment. Greywater is the wastewater generated in the bathroom, kitchen and laundry. Greywater is therefore the components of domestic waste water, which have not originated from the toilet. The opportunity exists for greywater to be reused to irrigate gardens. This will reduce the demand on quality ground and surface water supplies. Considering the dry environment in some parts of India such as Madhya Pradesh, Rajasthan, Andhra Pradesh, Delhi and Maharashtra and the sometimes limited supply of water available, it is important that water is used efficiently and conserved wherever possible. Reuse of greywater is therefore supported and encouraged by Government to help conserve water. However, this has to be accomplished without compromising community health, causing unacceptable environmental impact, or downgrading the amenity of our residential areas. Greywater must be reused in a beneficial manner for landscaping (i.e. to the plant rootzone) rather than simply disposal at a depth, which would not benefit landscaping.
Greywater comes from the bathroom, laundry and kitchen. Whilst greywater does not contain toilet waste it nevertheless generally contains the same pathogenic micro-organisms (though in much lower numbers) just from washing your hands, bathing and washing soiled clothing. Therefore, health authorities recommend caution when reusing greywater. The best means of addressing their concerns, without use of expensive and often un-reliable treatment and disinfection technologies is simply to irrigate greywater below the ground surface to avoid un-necessary human contact.
Whilst greywater will always contain some micro-organisms the health hazards from a multi dwelling greywater source are significantly greater than from a single dwelling greywater source. This is because within a single dwelling setting inhabitants already have intimate exposure to the same greywater whilst bathing and washing and essentially to their existing family unit's reservoir of micro-organisms, whereas exposure to greywater from multi dwelling sources has potential to expose an individual to micro-organisms not already present within their family unit and there a greater potential for spread of disease.
2.4.2 Rainwater Harvesting and Utilization
Rain is the ultimate source of freshwater. With the ground area around houses and buildings being cemented, particularly in cities and towns, rain water, which runs off from terraces and roofs, was draining into low-lying areas and not percolating into the soil. Thereby, precious rainwater is squandered, as it is drained into the sea eventually. Conservation of rainwater is known as "Rainwater Harvesting" through which monsoon run off can be utilized for domestic use which otherwise goes waste.
Rainwater harvesting is a system by which, the rainwater that collects on the roofs and the area around the buildings is directed into open wells through a filter tank or into a percolation chamber, built specifically for this purpose. Rainwater is collected directly or recharged into the ground to improve ground water storage.
"Collection of rainwater from paved or GI corrugated roofs and paved counts yards of houses of houses either, in storage tank or in the groundwater reservoirs is known as rain water harvesting".
This collected water serves as good source of water in the rural, urban and water scarce areas. Rainwater harvesting, in its broadest sense, is a technology used for collecting and storing rainwater for human use from rooftops, land surfaces or rock catchments using simple techniques such as jars and pots as well as engineered techniques.
2.4.3 Sustainable Water Management
Sustainable Development "Development that meets the needs of the present without comprimising the ability of the future generation to meets their own needs." (According to the Brundtland report). In essence this definition implies:
"Recognition of the essential needs-particularly of the world poor".
Concern for the establishment of social equity between generation and within generation.
Recognition of the limitation imposed by the capabilities of technology and social organization on the ability of the environment to meet present and future demands.
In relation to water the concept set out above can be interpreted as follows;
Water is a scarce resource which should be viewed as both a social and an economic resource.
Water should be managed by those who must use it, and on those who have an interest in its allocation should be involved in the decision making.
Water should be managed with in a compressive framework, taking in to account its impact on all aspects of social and economic development.
Sustainable development generally means addressing environmental, economic and social concerns, and roots back many years, e.g. the World Commission on Environment and Development (1987). Looking at EU policies, the Amsterdam Treaty in its Article 6 highlights the importance of integrating the environment into all Community policies, and the UN Economic Commission of Europe (UNECE) Aarhus Convention of 1998 on access to information and public participation in environmental decision making shows the need of governance aspects and public participation as key elements to sustainable development (Feldman et al., 2001). Also the recent EU Water Framework Directive (WFD, 2000/60/EC) internalizes a more complete concept of sustainability. The purpose of Sustainable Water Management (SWM) is simply to manage our water resources while taking into account the needs of present and future users. However, SWM is much more than its name implies. It involves a whole new way of looking at how we use our precious water resources. The International Hydrological Programme, a UNESCO initiative, noted:
"It is recognized that water problems cannot be solved by quick technical solutions, solutions to water problems require the consideration of cultural, educational, communication and scientific aspects. Given the increasing political recognition of the importance of water, it is in the area of sustainable freshwater management that a major contribution to avoid/solve water-related problems, including future conflicts, can be found."
Therefore, SWM attempts to deal with water in a holistic fashion, taking into account the various sectors affecting water use, including political, economic, social, technological and environmental considerations. Since the Mar Del Plata Water Conference hosted by the UN in 1977, SWM has been high on the international agenda. Later conferences and workshops have addressed the issue and have attempted to refine the concept as more and more research has been done in the area. The current understanding of SWM is based primarily upon the principles devised in Dublin during the International Conference on Water and the Environment (ICWE) in 1992, namely: (i) Freshwater is a finite and valuable resource that is essential to sustain life, the environment and development. (ii) The development and management of our water resources should be based on a participatory approach, involving users, planners and policy makers at all levels. (iii) Women play a central role in the provision, management and safeguarding of water resources. (iv) Water has an economic value and should therefore be seen as an economic good. These principles reflect the importance of water in our daily lives and the need for proper communication, gender equity, and economic and policy incentives to manage the resource properly.
2.5 Components of Wise Water Management
These users are typically the most vulnerable, e.g., rural communities and aquatic ecosystems. Historically and inevitably water resources planning management is focused on treated greywater and rainwater.
Wise water is a term used in such water management techniques to denote treated greywater and treated rainwater: Greywater requires more treatment than rainwater to reach an acceptable standard. The level of treatment required depends on the scale and purpose of use. At small scale, a two stage treatment consisting of filtration of coarse pollutants (hair and suspended impurities) followed by disinfection with chlorine, bromine or UV may be sufficient (Memon and Butler, 2005). Greywater recycling at the medium to large scales may be more viable but requires more complex treatment. Option includes biological aerated filters, membranes, bioreactors, UV treatment, titanium dioxide dosing, membrane aeration bioreactors and coagulation/flocculation with alum or ferric (Memon and Butler, 2005).
Greenwater (greywater and rainwater), regardless of the scale of recycling chemes or origin, could be a viable alternative water supply, and can potentially substitute potable water in some water uses within the house, with the obious exception of drinking water or food preparation. Studies have shown (Nolde, 2000) that service (green) water made available from rainwater or grey water system can be cost effective and with proper operation presents to hygienic risk or comfort loss for the consumer.
Rainwater usually carries small pollutants loads (depended interalia on location, roof building materials and collection system construction) and its harvesting system consists of three basic elements: the collection system, the conveyance system and the storage system. The main disadvantage is the unpredictable and often irregular supply which results in large storage space requirements (Dixon et al; 1999). Light treatment and disinfection is generally adequate for rainwater treatment to non potable standard.
A wise water management system improves:
(i) Rainwater use efficiency and hence yield potential, and
(ii) At the same time, improves green water resources, greywater (wastewater) reuses, by reduced run-off, thereby causing a reduction in flash floods, erosion and water turbidity, and increase ground water recharges. Wise water management techniques include all sustainable techniques and approaches to reduce surface run-off, increase water infiltration, reduction of water purchasing costs, reducing your drinking water consumption and your water bills, reducing the amount of sewage discharged to the oceans or river, irrigating your garden during a sprinkler ban, reduced septic emptying costs, recreased rate of freshwater extraction, reduced use of energy for waste water treatment, groundwater recharge and reduce soil infiltration.
The wise water management approach includes: (a) rainwater harvesting (b) reuse of greywater for toilet flushing, washing and gardens irrigation, (c) recycling of hand washing water for gardening and (d) implementation of Water Safety Plans (WSPs) and (e) development of NEERI Water Safety Club (NWSC) for system management.
2.5.1 Greywater
Historically, domestic greywater reuse was practiced to conserve water. However, social and economic constraints prevented its further development and integration in the urban water systems. It is likely that new innovations in water management will eventually lead to substantial changes in lifestyle, particularly if the use of water as a transport medium for our domestic waste is reduced or eliminated. The conventional paradigm of water/waste water management was characterized as supply driven, centralized and large-scale development. This approach led to over-exploitation or depletion of renewable water resources, mining of non-renewable groundwater resources and deterioration of water quality. The collection and disposal mind-set prevailed because of concerns over public health protection. Water-intensive and centralized sewer systems were built to remove wastewater from immediate environment of the communities using water as a transport medium. This paradigm is inadequate for sustainable water management. A need for a paradigm shift is necessary to ensure optimum utilization of resources. Wastewater and greywater (GW) recycling are emerging as integral parts of water demand management, promoting the preservation of high quality freshwater as well as reducing pollutants in the environment and reducing overall supply costs. Recent developments in technology and changes in attitudes towards water reuse suggest that there is potential for GW reuse in the developing world. GW represents the largest potential source of water savings in domestic residence. For example, the reuse of domestic GW for landscape irrigation makes a significant contribution towards the reduction of potable water use.
Greywater comes from the bathroom, laundry and kitchen. Greywater is the dilute wastewater stream originating from domestic activities such as showering, bathing, washing hands, tooth's brushing, dishwashing, washing clothes, cleaning and food preparation. The water contains some organic material, for example, food remains, with pathogens, and inorganic material, such as detergents, sand and salt (Balkema, 2003). The advantage of reusing greywater is that the supply is regular and not dependent on external phenomena (such as rain). As a result, the storage space required could be substantially smaller than the case of rain water systems. Moreover, the substitution of potable water with greywater used for purposes other than drinking, e.g., toilet flushing, floor washing, vehicle washing and garden irrigation, reduced demand and thus assists the preservation of valuable water resources (Nodle, 2000).
The main issues, relevant to the applicability of greywater systems include social acceptability and water quality. A freshly produced greywater usually does not have any objectionable odour. However, it requires early treatment after collection. If stored untreated greywater for long periods, oxygen deficient conditions will develop and scum will be formed that can float or sink in the collection Tank (Memon and Butler, 2005). Moreover, the bacterial population tends to increase with increased storage duration (Dixon et al., 1999). In general, treating greywater prior to recycling is more socially acceptable, and renders it suitable for more uses. It should be noted, however, that water quality standards for in house greywater reuse have yet to be defined in the UK.
Whilst greywater will always contain some micro-organisms the health hazards from a multi dwelling greywater source are significantly greater than from a single dwelling greywater source. This is because within a single dwelling setting inhabitants already have intimate exposure to the same greywater whilst bathing and washing and essentially to their existing family unit's reservoir of micro-organisms, whereas exposure to greywater from multi dwelling sources has potential to expose an individual to micro-organisms not already present within their family unit and there a greater potential for spread of disease. Greywater contains traces of oils, fats, detergents, soaps, nutrients, salt and particles of food hair and lint etc that can quickly clog a greywater subsurface irrigation system. In contrast, greywater from the bathroom and laundry account for the majority of the greywater stream but generally contribute little of the components that cause clogging and therefore generally requires only removal of suspended particles such as lint and hair. The diversion of greywater from the house and into the garden has become an extremely popular way of irrigating our precious green spaces in these times of low rainfall and water restrictions, and, when done correctly, is an excellent way of saving water and money. Recycling household greywater for use on garden beds is an excellent way of saving water and saving money. Unlike rainwater, which is seasonally available, greywater is available every time you shower or wash. The average house creates up to 83,000 liters of greywater per year.
2.5.1.1 Concept of greywater reuses
Greywater represents a valuable renewable resource that can allow significant household water savings and reduces demand for potable water. Reusing greywater also reduces discharge to the sewerage system, which can lead to community cost savings through reduced pressure on sewerage treatment systems and infrastructure. Greywater consists of wastewater from showers, baths, spas, hand basins, washing machines, laundry troughs, dishwashers and kitchen sinks.
Water can be classified as freshwater, greywater and black water based on characteristics and potential for (re)/use as presented in Table 2.2.
Table: 2.2 Types of Water and Possible Uses
Asano (2004) reiterated (re)/use of treated wastewater in many forms such as direct potable, indirect-potable, direct-non-potable and indirect non-potable to overcome water scarcity as depicted. The technologies are available to make sewage potable; however, cost effectiveness will be a key parameter in deciding feasibility of waste water treatment and reuse.
Potential of greywater reuse
Reuse of greywater serves two purposes:
Reduces freshwater requirement
Reduces sewage generation
The amount and quality of greywater will in part determine how it can be reused. Irrigation and toilet flushing are two common uses, but nearly any non-contact use is a possibility. Toilet flushing can be done either by direct bucketing or by pumping treated greywater to an overhead tank connected by suitable piping to the toilets. Possible uses of treated greywater are presented in Table 2.3.
Table: 2.3 Use of Greywater
Greywater for agricultural irrigation
The use of greywater for agricultural irrigation purposes is occurring more frequently because of water scarcity and population growth (Bernard et al., 2003). The treated greywater can be supplied for irrigation of indoor plants as the greywater is most suitable for this purpose. However this application must meet the stringent requirements from possible exposures to greywater. The treated greywater can also be used for irrigating agricultural crops and turfs and for maintaining decorative fountains or landscape impoundments.
Agricultural irrigation using greywater to support crop production is a well-established practice in arid and semiarid regions. A significant portion from existing greywater can meet the demand for agricultural irrigation. A number of guidelines for the quality of reclaimed water for irrigation can be found in the references (USEPA 1992 and Lee et al., 2003). The application of the greywater system is therefore of particular importance, hence the excess water in the system can be applied elsewhere for which the system has to be carried out properly so that the practice of reclamation and reuse can bring significant environmental and health benefits, including the increased agricultural productivity through irrigation.
Augmentation of potable water supplies through aquifer recharge.
Recycling plant nutrients thereby reducing eutrophication.
Reserving drinking water supplies by substituting with treated greywater e.g. landscape irrigation, toilet flushing, industrial uses and cooling water.
The excess amount of the treated greywater can be made suitable for irrigating lawns, trees and ornamental food crops. Though irrigation methods in the greenhouse may differ greatly from outdoor irrigation, several guidelines for use of greywater apply to both situations. The guidelines below should be followed when irrigation is practiced with treated greywater:
Apply greywater directly to the soil, not through the sprinkler or any method that would allow contact with the above ground portion of the plants which are eaten uncooked.
Root crops which are eaten uncooked should not be irrigated with greywater
Plants that thrive only in acid soil should not be watered with greywater, which is alkaline.
Use greywater only on well- established plants.
Disperse greywater over a large area and rotate with freshwater to avoid build-up of sodium salt.
Site selection
In the process of assessing the suitability of sites for constructing greywater treatment system, important considerations are as below:
Approximate size of 15 - 20 m2 land in the school or institute campus for reuse system has been considered.
Topography and natural slope: the topography of the sites and contours can be established using standard surveying procedures. The slope of the site is an important factor in controlling surface ponding, runoff and erosion. A minimum of 2% slope of area is recommended.
Soil type: Soil type and properties are the key factors in the design and operation of greywater reuse systems. The main characteristics necessary for the evaluation of the soil for the purpose of greywater reuse are soil texture, soil structure, corrosiveness, submergence, infiltration rate through topsoil and percolation rate in the sub-strata. Percolation rates can be determined using percolation tests and compared with textural classification charts. Infiltration rates can be determined using a cylinder infiltrometer (Christov et al., 1995). As sandy lighter soils can absorb more greywater, and heavier soils with a high clay content absorb less (Greenhouse People's Environmental Centre, 2002) therefore soil having structural stability i.e., stable clay/silt, hard strata soil is recommended for greywater reuse system construction. Black cotton soil and sandy soil should be strictly avoided.
2.5.1.2 Composition of Greywater
(i) Greywater from bathroom
Water used in hand washing and bathing generates around 55-60% of total greywater and is considered to be the least contaminated type of greywater. Common chemical contaminants include soap, shampoo, hair dye, toothpaste and cleaning products. It also has some faecal contamination (and the associated bacteria and viruses) through body washing.
(ii) Greywater from cloth washing
Water used in cloth washing generates around 34% of total greywater. Wastewater room the cloth washing varies in quality from wash water to rinse water to second rinse water. Greywater generated due to cloth washing can have faecal contamination with the associated pathogens and parasites such as bacteria.
(iii) Greywater from kitchen
Kitchen greywater contributes about 11% of the total greywater volume. It is contaminated with food particles, oils, fats and other wastes. It readily promotes and supports the growth of micro-organisms. Kitchen greywater also contains chemical pollutants such as detergents and cleaning agents which are alkaline in nature and contain various chemicals. Therefore kitchen wastewater may not be well suited for reuse in all types of greywater systems.
2.5.1.3 Characteristics of Greywater
There is variation in chemical and microbial quality of greywater depending on source types. A typical qualitative composition of greywater is presented in Table 2.4.
Table: 2.4 Characteristics of Greywater
(Source: Wright, 1986 & Errikson, 2002)
The chemical characteristics of greywater typically are presented in Table 2.5. Treatment requirements vary based on chemical characteristics and intended use of treated greywater.
Table: 2.5 Typical Characteristics of Greywater
Parameter
Unit
Greywater Ranges
pH
--
6.6-8.7
Conductivity
mS/cm
325-1140
Turbidity
NTU
22-200
Suspended solids
mg/L
45-330
Sulfate
mg/L
7.9-110
Total phosphorus
mg/L
0.6-27.3
Nitrite
mg/L
< 0.1-0.8
Ammonia
mg/L
< 0.1-25.4
Sodium
mg/L
29-230
Total Kjeldahl nitrogen
mg/L
2.1-31.5
BOD5
mg/L
90-290
(Source: Jeppersen and Solley, 1994)
The microbiological quality in terms of number of thermotolerant coliforms of greywater from various sources in an is presented in Table 2.6. Thermotolerant coliforms are also known as faecal coliforms (expressed as colony forming units per 100 ml) and are a type of micro-organism which typically grow in the intestine of warm blooded animals (including humans) and are shed in millions to billions per gram of their faeces. A high faecal coliform count is undesirable and indicates a greater chance of human illness and infections developing through contact with the wastewater. Typical levels of thermotolerant coliforms found in raw sewage are in the order of 106 to 108 cfu/100ml.
Table: 2.6 Faecal Coliforms in Greywater
(Source: Jepperson et al., 1994)
Where,
A- Family without children
B- Families with children
C - Other study quoted cfu- colony forming units/100ml
D - Kitchen and bath only MPN- most probable number
Note: For all practical purposes, cfu can be considered similar or of the same magnitude order as MPN.
2.5.1.4 Quantification of Greywater
Determination of greywater generation and flow rate is the first requirement in the design of greywater collection, treatment and reuse system. Reliable data on existing and projected flow rate must be available for the cost-effective greywater treatment system design. The possible reuse options as previously described also determines treatment design. Following methods are proposed for quantification of greywater:
[A] Direct method
(i) Water meter
In the water meter method, a meter is provided at the outlet of the drain connecting bathrooms, kitchen and cloth washing place (laundry). If not possible, the meter can be placed at the inlet of the greywater collection tank which can be connected to bathroom, kitchen and laundry. Small plumbing modification in the piping system will allow collection of greywater system which can be easily measured. This system can be fitted in residential schools where variation in greywater quantity is not expected.
(ii) Bucket method
This is the simplest form of greywater quantification where in greywater is collected in a bucket of known volume at the outlet of bathroom, laundry or kitchen. This method is cheap and suitable where greywater quantity remains almost constant for a substantial time period. The precautions are required to avoid any human contact with greywater. The method is described below:
Identify outlet
Keep a 20 liters bucket at outlet of bathroom and laundry
Start stop watch and measure time for filling of 20 liter bucket
Measure during 24 hour cycle
Measure once per month
Measure only during February, March and April
Find out average value of greywater per day
[B] Indirect method
Indirect method also includes correlation between a variable and greywater generation. As mentioned earlier, greywater quantity is about 50-60% of total water consumption. The quantity of water consumed can also be used to quantify greywater.
2.5.1.5 Greywater treatment options
Greywater reuse methods can range from low cost methods such as the manual bucketing of greywater from the outlet of bathroom, to primary treatment methods that coarsely screen oils, greases and solids from the greywater before irrigation via small trench systems, to more expensive secondary treatment systems that treat and disinfect the greywater to a high standard before using for irrigation. The choice of system will depend on a number of factors including whether a new system is being installed or a disused wastewater system is being converted because the household has been connected to sewer. Options for reusing greywater are listed below. The greywater treatment options as shown in Fig: 2.6 include anaerobic sludge reactors, septic tanks, oxidation ponds etc.
Figure: 2.6 Greywater Treatment Options
Among the above mentioned options the filtration was followed due to their advantages
mentioned below:
Easy operation and maintenance
Economical
Provides extensive physical treatment
Treated greywater is of better quality
Use of locally available filter media
No requirement of external energy source
Anaerobic process require a methogenic state to complete the destruction of vegetable fatty acids and removal of ammonia
Oxidation ponds are not a complete process and requires services of waste stabilization ponds
Primary treatment system
In primary treatment system, a sedimentation tank is used to coarsely screen out oils/greases and solids prior to reuse. This system is recognized as an economically attractive option for greywater reuse because it requires minimal maintenance, and chemicals.
Secondary treatment system
In secondary treatment system, Chemical and Biological treatment process are used to remove most of the organic matter. This reduces health risk at end use with human contact and provides additional safety for reuse. This system is generally more expensive, due to the initial establishment costs associated with the further treatment needs and the periodic maintenance costs.
Tertiary treatment system
Tertiary treatment processes further improves the quality of greywater or polish it for reuse applications. Fixed film biological rotating drums, membrane bioreactors, biologically aerated filters, activated sludge and membrane treatment systems are all included in this category. Whilst utilized on larger scales for more general effluent applications, the other tertiary treatment technologies mentioned lack sufficient studies into greywater applications and current literature indicates that costs are high (Al-Jayyousi, 2003).
Biological treatment system
This level of treatment involves utilising the biological content in greywater to reduce microbial contamination, suspended solids, turbidity and nutrients (nitrogen and phosphorous). The treatment process requires a significant level of automation and energy to power the aeration technology as well as pumps and disinfection systems.
Greywater is characteristically low in nutrients and this would inhibit the efficiency of biological treatment systems for application in greywater treatment. Consistency in treated greywater quality can also be achieved through greater storage volumes which assist in the biological treatment process (Al-Jayyousi, 2003). However, the consistency of biological treatment systems could vary greatly according to the types of chemicals used at greywater sources. Some substances or products used such as laundry washing products, soaps or shampoos with high amounts aluminum or zeolite could poison or hinder the biological process (Christova-Boal et al., 1995).Other examples of greywater reuse systems that do not incorporate typical primary or secondary treatment include systems that physically capture/filter out solids from specific greywater streams prior to reuse and will require ongoing maintenance to regularly clean the system. Primary and secondary greywater treatment options are described in Table 2.7 and greywater quality variables Table 2.8.
Table: 2.7 Greywater Treatment Options
Table: 2.8 Treatments for Greywater Quality Variables
(Source: Wright, 1986)
Odour and colour control
There is a possibility of odour generation in greywater treatment system due to the following;
A slime layer will develop on the submerged walls of filters, collection sump and possibly in sedimentation tank and as velocity of the greywater through the system sometime is too low to scour the sides.
If aeration is not sufficient dissolved oxygen will reduce substantially and only anaerobic bacteria will attach to the slime layer.
The anaerobic condition will lead to release of odorous compounds from the system and build up of hydrogen sulfides may result in a situation hazardous to human health.
Odour control
Good design and maintenance practices will reduce odour problems in greywater treatment system without the use of chemical addition or air treatment. However, the following measures are recommended to minimize odour problems.
A minimum slope of 2-3 % should be provided so as to ensure sufficient flow through system when in operation.
Baffles should be provided at the entrance of sedimentation tank and in collection sump for aeration.
The closed conduit system should be avoided. If a closed conduit system is unavoidable, length should be minimal with adequate velocity to scour the pipe.
Deposited solids should periodically be removed from sedimentation tank.
Natural coagulants such as ground seeds of drumsticks should be added to sedimentation tank.
Addition of chemicals such as calcium nitrate, hydrogen peroxide, potassium permanganate, hypochlorite and chlorine added to the system to oxidize the sulphate bearing ingredients of greywater. This is only necessary if the system cannot be designed in such a way to prevent formation of anaerobic conditions.
Filters should be washed with clean water and filter media should be periodically replaced as mentioned in O&M.
Chlorination of final effluent also helps in minimizing odour.
Collection sump can be covered and vent pipe can be provided to let out the odourous compounds.
2.5.1.6 Components of Greywater Treatment Systems
Advances in the effectiveness and reliability of wastewater technologies have improved the capacity to produce reused water that can serve as alternative water source in addition to meeting water quality protection and pollution abatement requirements (Lazarova, 2000). In southern European Union (EU) countries, additional resources brought by water reuse can bring significant advantages to agriculture e.g. crop irrigation (Angelakis et al., 2003). A number of technologies have been applied for greywater treatment worldwide varying in both complexity and performance (Jefferson et al., 2001). The following greywater systems considering non-contact application are considered in this project work:
[A] Primary treatment /pre-treatment
Screening
Equalization
[B] Secondary treatment
Gravel filtration
Sand filtration
Chlorination
[A] Primary Treatment Systems
(i) Greywater Diversion Devices
These systems do not store or treat greywater and as such are best to reuse greywater for sub-surface applications. The simplest forms of primary greywater reuse systems are best described as greywater diversion devices (Ludwig, 1994) and are the most economical. A simple plumbing device diverts greywater in the wastewater drainage line to a subsurface garden irrigation system via gravity without any external energy. This system does not treat the greywater and as such the sub-surface garden irrigation system must be able to cope with fouling material such as hair and lint (Ludwig, 1994). The land patches irrigated directly with greywater are termed as mini-leachfields which filter the solids and allow sub-surface infiltration. In these applications the soil treats the greywater and consideration must be given to the type and depth of soil available to complete the process.
(ii) Primary (Pre-treatment) and Secondary Greywater Treatment Systems
Primary (pre-treatment) and secondary greywater treatment systems are useful in hostels, schools and residential complexes to treat greywater to the tune of 1000-2000 l/day. A potential treatment scheme is shown in Fig. 2.7 The function of various treatment units are presented in Table 2.9.
.
Fig: 2.7 Greywater Treatment Scheme
