Plumbing Africa August 2018 - Page 49

HEALTH AND SANITATION The purpose of pre-filtration is to significantly cut down on maintenance by preventing organic build-up in the tank, thereby decreasing microbial food sources. If rainwater is not pre- filtered, a large amount of organic matter in the form of leaves and dirt can enter the storage tank. Aerobic bacteria begin to consume the organic matter and use up all the dissolved oxygen. This sets up anaerobic conditions that allow anaerobic bacteria to predominate, resulting in odour. Other benefits of pre-filtering rainwater are reduced sediment build-up at the bottom of the storage tank and less tank maintenance. • Leaf screens Leaf screens are installed over either the gutter or downspout to separate leaves and other large debris from rooftop runoff. Leaf screens must be regularly cleaned to be effective; if not maintained, they can become clogged and prevent rainwater from flowing into the storage tanks. Built-up debris can also harbour bacteria and enhance their growth within gutters or downspouts. • Gutter guards or screens Gutter screens can be installed on the gutter to filter debris before they enter the gutter. One advantage of gutter screening is the large filtering surface area, which can reduce maintenance of the filter surface. Some higher-quality gutter screening is nearly self- cleaning and requires very little maintenance. The micro-mesh screen can filter debris in the 80–100-micron size, which is beneficial for potable or indoor fixture systems that require superior filtration. • Downspout filters (leaf catchers) These filters are placed either at the top of the downspout where it meets the gutter, or somewhere along the length of the downspout. These filters generally only provide coarse filtration of 3175–1587 microns and should only be used for rain barrel systems. A few models can filter to 280 microns and make good pre-filters for irrigation systems and indoor non-potable uses. • First-flush diverters First-flush diverters direct the initial pulse of rainfall away from the storage tank. While leaf screens effectively remove larger debris such as leaves, twigs, and blooms from harvested rainwater, first-flush diverters can be used to remove smaller contaminants such as dust, pollen, and bird and rodent faeces. Simple first-flush diverters require active management, by draining the first-flush water volume to a pervious area following each rainstorm. First-flush diverters may be the preferred pre- treatment method if the water is to be used for indoor purposes. • Insect screens The inlet of the tank should incorporate a mesh cover and a strainer to keep leaves from entering the tank and to prevent access of mosquitoes and other insects. The overflow should also be covered with an insect-proof cover such as plastic insect mesh wired around the pipe. POST-STORAGE TREATMENT DEVICES The fundamental difference between centralised water treatment works and HWT is not the underlying mechanism for treating the water, but the point where such treatment is implemented. While the former is a combination of treatment methods, the latter (HWT) tends to rely heavily on a single approach. These PRE-STORAGE TREATMENT DEVICES Pre-storage treatment methods are required to keep sediment, leaves, and other debris from entering the RWH system. Leaf screens and gutter guards meet the minimal requirements for pre-filtration of small systems, although direct water filtration is preferred. All pre- filtration devices should be low-maintenance or maintenance-free. 47 Continued on page 49 >> August 2018 Volume 24 I Number 6