Discuss over-view of lecture – I can a brief background on rainwater harvesting, and how it is used, discuss why rainwater may need to be treated, when its not necessary, and the four main types of treatment: roofwashers and strainers, disinfection (ozone, UV or chlorination); filtration; and pH adjustment
According to the National Hydraulics Research Institute of Malaysia. IR. AHMAD JAMALLUDDIN SHAABAN. Water consumption was 12.5 billion in 2001, so only 2% of water used.But.. Malaysia still have water supply disruption?? (1998 drough t brought unpleasant water supply disruptions to 1.8 million residents of Klang Valley) drought residents
Uses include irrigation, toilet flushing, and in some cases laundry. Water may or may not need to disinfected. As an example, it is often considered that rainwater used for irrigation does not need treatment. However, if bird droppings on the roof cause legionnaire's disease or other pathogens to multiply in the water tank, and during irrigation, the water is vaporized it can cause bacteria and viruses to spread. I will be talking mainly about rainwater treatment, and assume that the rainwater is being used in applications where treatment is desired.
According to the National Hydraulics Research Institute of Malaysia. To increase soil moisture levels for urban greeneryTo increase the ground water table through artificial recharge Contribute in overcoming shortage of water during extreme droughts
Ensuring the quality of rainwater collected requires sensible maintainance of rainwater tank and roof catchments. The following simple steps can be taken to help improve rainwater quality:
Roof washer: This is a purpose built combination of a screen to collect debris that may have fallen on the catchmentarea during dry periods between rainfalls and a stand pipe (or a small container) of sufficient volumetric capacity to receive and by-pass the first flow of rain andwash away any dirt, bird droppings etc. that may have collected on it before collecting clean rainwater into the storage tank. It is a can be a simple device with no moving parts, or a commercially available device that is automatic. The manual onesrequiree occasional attention to clear away accumulated debris if there is any. The device consists of a funnel with a wire mesh screen fitted on it, with a standpipe of 150 to 200 mm diameter underneath (or a container),that collects the first flush of rainfall. Once it has filled up with the first flush of water, the rest of the water overflows into the downspout connected to the storage tank.
All roof washers must be cleaned.Without proper maintenance they notonly become clogged and restrict theflow of rainwater, but may themselvesbecome breeding grounds for pathogens. Two types – one without floating Styrofoam ball (on left) and one with ball.
Roof washer: This is a purpose built combination of a screen to collect debris that may have fallen on the catchment area during dry periods between rainfalls and a stand pipe (or a small container) of sufficient volumetric capacity to receive and by-pass the first flow of rain andwash away any dirt, bird droppings etc. that may have collected on it before collecting clean rainwater into the storage tank. It is a simple device with no moving.
Ball float type automatically diverts water when stand pipe is full
Storage tanks must be opaque, either upon purchase or painted later, to inhibit algae growth. For potable systems, storage tanksmust never have been used to store toxic materials. Tanks must be covered and vents screened to discourage mosquitobreeding. Tanks used for potable systems must be accessible for cleaning.
Polyethylene tanks arecommonly sold at farm and ranch supplyretailers for all manner of storage uses.Standard tanks must be installed aboveground. For buried installation, speciallyreinforced tanks are necessary towithstand soil expansion andcontraction. They arerelativelyinexpensive and durable, lightweight,and long lasting. Polyethylene tanksare available in capacities from 50gallons to 10,000 gallons.
Polyethylene tanks are light.
Ferro cement consists of a thin sheet of cement mortar which is reinforced with a cage made of wire mesh and steel bars. Because Ferro cement is structurally more efficient than masonry, the thickness of the walls of the container are as low as 10 to 15 mm. Ferro cement components can be casted in any shape using suitable molds. The technology is extremely simple to implement, and even semi-skilled work persons can learn it with ease. Ferro cement requires only a few easily available materials - cement, sand, galvanized iron (GI) wire mesh, and mild steel (MS) bars - in small amounts compared to masonry and RCC. Acid pH can be a problem with Ferro cement tanks.
Rainwater is relatively pure, except at some industrialized locations where acid rain could pose as a threat. If heavy rainfall persists fora long period, only the initial part of rainwater is polluted with acid, the remainder of the precipitation shall usually be acceptable. Generally the rain water collected is safe for consumption as long as the protection measures are taken. This is based on samplings conducted on several places. For example in 2006 sampling conducted on 54 rain harvesting system in BatuPahat District, only two non-compliance of the Drinking Water Quality Standard were detected; one sample was found to have total coliform and another one was found to haveturbidity higher than 5 NTU (nephelometric turbidity unit). All other samples complied with the standard for the parameter pH and E-coli. However it is important to note that most of the pH readings were at the lower part of the standard range that is 6.5-9. Apparently it is inline with the finding reported by Malaysia Meteorological Department (MET, 2005) where by the average pH of rain through out the Malaysia is below 5.2, therefore a little bit acidic. National Standard For Drinking Water Quality use by Ministry of Health has stated the pH standard should be between 6.5 and 9.0 (MOH, 2004). Low pH will increase the potential of corrosion which could break the rain harvesting system and disrupt the water supply (WHO, 2007). There is also a possibility increase in ingestion of metal from plumbing and pipes. Therefore low pH of rain reported should cause for concern and research is needed to determine extend of its impact. Taha, M.Pauze.MEngineering Services Division,Ministry of Health Malaysia
Rainwater can be corrosive
Acidic waters on contact with Calcite slowly dissolve the calcium carbonate media to raise the pH which reduces the potential leaching of copper, lead and other metals found in typical plumbing systems. Periodic backwashing will prevent packing and maintain high service rates. Depending on pH and service flow, the Calcite bed will have to be periodically added to as the dissolved calcite depletes.As the Calcite's calcium carbonate neutralizes the water, it will increase hardness and a softener may become necessary after the neutralizing filter. Advantages: High uniformity coefficient for maximum contact for con-trolled pH correction Slower reacting. Physical Properties: Color - Near White Density - 100 lbs./cu. ft. Composition - CaCO3, 95% minimum- MgCO3, 3.0% maximumConditions for Operation: pH - 5 - 6 Bed Depth - 24 - 30 in. Backwash Rate - 8-12 gpm. sq. ft. Backwash Bed Expansion - 35% of bed depth Service Flow Rate - 3 -6 gpm/sq. ft. invariably give satisfactory results."
How it Works— water enters the top through the backwash controlvalve, and flows down through the calcite media from top to bottom. ThepH is neutralize at this point. At the bottom, the water flows in to thedistributor screen and up through the distributor tube, and outto the household piping. During a backwash, the control valve re‐directsthe water down the distributor tube and up through the calcite media,and out to drain. The calcite expands and sediment is flushed to drain.The automatic weekly backwash keeps the media clean and prevents thecalcite media from becoming solidified.
UV light has been used in Europe fordisinfection of water since the early1900s, and its use has now becomecommon practice.Bacteria, virus, and cysts are killed byexposure to UV light. The water must gothrough sediment filtration before theultraviolet light treatment becausepathogens can be shadowed from the UVlight by suspended particles in the water.In water with very high bacterial counts,some bacteria will be shielded by thebodies of other bacteria cells. Ultraviolet water purification is a rapid method of water disinfection without the use of heat or chemicals. Ultraviolet Purifiers utilize germicidal ultraviolet lamps that produce short wave radiation lethal to bacteria, viruses and other microorganisms present in water. 1: The water enters the purifier and flows into the annular space between the quartz sleeve and the outside chamber wall.2: The wiper segments induce turbulence in the flowing liquid to assure uniform exposure of suspended microorganisms to the lethal ultraviolet rays.3: Translucent sight port provides positive indication of germicidal lamp operation.4: The wiper assembly facilitates periodic cleaning of the quartz sleeve without any disassembly or interruption of purifier operation.5: Water leaving the purifier is instantly ready for use.
Chlorination is mentioned here more for its historical value than for practical application. Chlorine has been used to disinfect public drinking water since 1908, and it is still used extensively by rainwater harvesters in Hawaii, the U.S. Virgin Islands, and in older rainwaterharvesting systems. Chlorine must be present in a concentration of 1 to 2 ppm for at least 20 minutes to achieve disinfection.
Advantages of ozone are oxidation of pesticides and herbicides when used with UV sterilizers. Mixed oxidation is a powerful method to destroy pathogenic organisms and oxidize organic compounds.
Dual use – only water for potable use is passed through ozone.
Can be controlled by ORP. Combination of ozone and UV offers mixed oxidation treatment for pesticides and herbicides.
1 micron for cyst removal. Birds may spread cysts.
Treatment options for rainwater harvesting systems
Treatment Options for Rainwater Harvesting Systems For more information go to: www.cleanwaterstore.com
Rainwater often used for non-potable water applications
Benefits of RainwaterProvide water for rural areasReduce the dependence and demand of public water supplyReduction of water billsAdditional water supply for fire protection or emergency useReduce land erosion and floodingReduce salt accumulation in soil which can be harmful to root growth
Rainwater quality affected by atmospheric contaminationCarbon dioxide (CO2) levels - affect pH, creating acidic waterPollution from industry - industrial pollution such as sulfur dioxidePollution from agriculture – pesticides and herbicides
Rainwater quality affected by roof or other catchment surfaces
Maintaining Roof Water Quality• Regularly inspect and clean gutters, roof catchments and tank screens.• Remove overhead branches and clear trees near roof.• Consider installing gutter screens or guards.• Ensure tank does not become a mosquito breeding site by preventing access and cleaning screens regularly.• Examine tank for accumulation of sludge every year and remove by siphon or by empting the tank.• Shock sanitize by adding 40 mm of liquid bleach or 7 grams of granular calcium hypo-chlorite per 1000 liters of water.