The appropriate exploitation and clearance of muck is one of the most significant problems presently confronting sewer water treatment plants. Practically all sewer water treatment plant operators confront the issue of storing and casting away bio solids. The costs of landfills are shooting up abruptly; burning permissions are costly and complex to obtain, and land use is restricted by the accessibility of allowable land. On the other hand, reed bed construction technology renders lasting storage and quantity decreases of biological solids to alleviate these headaches.
Reed bed technology is extensively utilized all over Asia, Australia, and Europe and in more than fifty locations in the United States. Great interest is also being expressed in Canada. Reed bed technology has a low price of entry and minimal daily functional and upkeep costs. The arrangement cuts down water content, reduces solids, and renders adequate storage time to steady bio solids preceding their removal.
A reed bed is basically a pond filled up with gravel of varied dimensions with reeds budding on the outside. Reed beds are classified as horizontal beds or vertical beds. In horizontal beds the water enters at one end and runs horizontally to the exit accumulator, whereas in vertical beds the water runs down perpendicularly through the bed. Vertical beds fill up and drain, oxygenating the bed as they work, but horizontal beds remain full most of the time and depend on the reeds to extract oxygen downward into their roots to nourish the aerobic microbes that keep the water smelling clean. This is where sewage sludge treatment in reed beds plays a significant role.
What is a Reed Bed?
A reed bed is fundamentally a canal lined with a water-resistant tissue layer that is filled up with gravel and planted with macrophytes, i.e. reeds, and utilized to handle sewer water. Effluent, black or grey, is directed through the root region of the reeds where it goes through treatment. Inlet and outlet pipe works are placed beneath the gravel surface so that the water perpetually stays under the gravel surface, thus barring human vulnerability to the effluent, the mosquitos engendered, and bitter odors.
Prior to entering a reed bed, all solids must be automatically separated from the water, which then runs through one or more beds filled up with beds of gravel, sand, and appropriate plants. Sewer water is scavenged by straining it through these layers, then by biological and chemical simplification of wastes. This decline is triggered by bacteria and microorganisms located on the roots and surfaces of the caryopsis (“dry fruit” or grain).
How Do Reed Beds Work?
Reed beds utilize general reed plants like phragnmites communis (the common reed) to remove water contents from solids in a restricted area. Nature’s very old processes are phragmites, and these have been tailored by man in the clash against contamination. The reed beds can be of any form to have room for obtainable land considerations and regions. Particularly planned ponds with underground drains covered up by a sand and gravel mix are built and filled up with reed plants.
Altered muck drying beds also work well and are perfect to transform into reed beds. They already have walls, beds of sand and gravel, an underground drainage arrangement which gathers and carries off filtrate, and an impermeable membrane lining.
Solids are forced into the reed beds. Dewatering takes place through vaporization, plant transpiration, and transfusion. The decanted water oozes through the underside of the bed, and via the beds of sand and gravel, and flows into the underground drains, moving back to the effluent treatment plant for resultant treatment. Throughout dewatering the solids alter from liquid to 6” of solids and water when then contract to ½” of solid cake. The cake is left behind in the bed and the procedure is repeated.
Basic Parameters for Reed Bed Design
Reed beds should be planned to have a sewer water dwelling time of five to seven days and can vary between 300-1000mm in depth. The ratio of dimensions of a reed bed should be between 3:1 and 1:1. If setting up a spherical reed bed, it is sensible to fix an innermost sump and strongly think about setting up inlet and outlet baffles to avert bypassing of sewer water in the reed bed and a potential decrease of treatment functioning.
Several reed beds hold 10-20mm gravel as a means for the main body of the reed bed, even though some reed beds contain a top stratum of sand for implanting the reeds. Blockage owing to solids in the influent can be reduced by setting up a sewer water strain on the passage of the grey water/septic tank.
Wastewater gets into the reed bed thru the inlet pipe located at a height beyond the outlet pipe, and disseminates the effluent as consistently as feasible into the gravel. Some reed beds utilize punched T-junctions prepared from 100mm PVC sewer grade pipe, while others use pierced 300mm crested, perforated storm water pipes. It is significant to avoid spouting of waste matter and the escape of smells. Hence, the inlet pipe should be wrapped up adequately. Big 50/100mm-width rocks can be laid around the inlet and outlet pipes to let the waste matter diffuse effortlessly and rapidly, to reduce blockage and make inspection for root integrity easier. (Some pipe fitters apply railway ballast for this purpose.)
How to Construct Reed Beds
A variety of different building techniques can be used in the building of reed beds. The majority of them are trouble-free and low-cost methods. Nonetheless quality and strength are dominant, and a refined design must be used. A cascading structure is well fitted to a moderate slope and would fend off digging of unnecessary quantities of soil in the groundwork for the building course. Concrete floors must then be streamed at a precise altitude variation of 0.4m, to avert problems in building the walls. The complete horizontal alteration desirable to keep the water uniformly within the reed beds can be attained utilizing a spirit level. Masonry must be accurate, and the cement should be permitted to dry completely as this step-ups constancy against high force on the walls formed by the weighty load inside. Inlet and outlet pipes for both reed beds must be installed at accurate heights. The slope can be leveled out utilizing shelves cut to the right size and set on the side of each wall. Waterproof membranes can be utilized to surface the inside of each bed. Cheap substitutes like plaster or tar can also be used.
Filling Up and Planting the Reed Bed Arrangement
As soon as the reed bed arrangement is constructed, it should be permitted to dehydrate really well. It has to be then filled with levels of 0.1 – 3mm round-shaped grain or sand with a hydraulically conduction kf between 10-3 and 10-4 m/s. Loam, clay, or other interrelated stuff should never be applied as this will ensue in dysfunction of its permeating function, blockage and, eventually, disintegration. The material has to be laid freely in the watershed of each bed, completely avoiding any solid crush. The reeds are embedded one foot on center all over the bed. Aerobically steadied muck is normally put on consistently through a grid-perforated cover. Mucks must be well steadied, 60% vaporized or less to be utilized productively with reed beds. The best application rates vary between two and four percent solids.
Operation and Care for a New Reed Bed
Immediately after planting, the reed bed has to be filled up with the subsidiary effluent to keep the scheme from dehydrating and to aid the plants in adjustment to their new surroundings. Consequently, it must be checked that the inlet, outlet, and all other pipe works are functioning. It will take no less than two months for the reed bed to attain stability in its usual cycle of development and converting, after which time it will start working at its utmost capacity, thus rendering established bacteria with oxygen and assisting them to reprocess waste water expeditiously.
Reed beds have comparatively low operating costs when compared with established biological treatment systems. As flow by the system is regulated by gravitation, there are no prerequisites for pumping as soon as the wastewater is in the reed bed. Likewise, as a natural process is helped by the reeds, there is no requirement for blowers to ventilate the system. Per se, there are no automatic or electrical necessities.
Reed beds have a high level of physical, chemical, and biological density. The management of wastewater is attained by a combining of the microorganisms and the corporal and chemical attributes of the solid media and the reeds, inside the reed bed. Furthermore, wastes are caught and altered by physical and chemical paths.
Due to the low level of technical features for reed beds, there is no prerequisite for well-trained operators. As the degradation of the effluent takes place inside a solid matrix, it should free from odor. Reed beds provide high flexibility for both the density and content of wastewaters as these schemes have a high variety of microorganisms. Reed beds may acclimatize to different kinds and unstable shock masses of effluents, including complicated waste waters comprising organic compounds like disinfected hydrocarbons, dyestuffs and sulphur comprising aromatics, and hard metals and pathogens.
Environmental Protection Agency – 2005
Tchobanoglous, G. & Burton, F., Wastewater Engineering: Treatment, Disposal, & Reuse, Third Edition, Metcalf & Eddy, Inc., McGraw-Hill, Inc.
David Giraldi and Renato Iannelli - Short-term water content analysis for the optimization of sludge dewatering in dedicated constructed wetlands (reed bed systems)