Since treatment in a sand bioreactor is accomplished by natural flow through a bed of sand, particles in the wastewater are easily filtered out in the sand and can quickly clog the bioreactor. Primary settling in a septic tank or clarifier is required to reduce the risk of surface clogging.
Septic tank effluent filters and screens around dosing pumps have also proven effective in protecting sand bioreactors from solids that escape the settling tank. Protecting sand bioreactors from excess solids is especially important for buried sand bioreactors where periodic observations and management are difficult.
Fortunately, most solids carried over from septic tanks or clarifiers are biodegradable. For ultimate biodegradation of open or covered bioreactors, raking of the surface to incorporate the solids into the beds of bioreactors can be practiced on a regular basis. In this way, a sand bioreactor can recover from occasional doses of solids which may occur during high flow periods.
Greases from restaurants and other food handling operations can quickly clog sand bioreactors. Removal of fats from wastewater through grease traps is currently recommended. Ongoing research on using sand bioreactors for high grease-content wastewater is summarized in Box 2 below.
BOX 2Research is being conducted at The Ohio State University and elsewhere on how to use sand bioreactors to renovate wastewaters that contain grease. Some of the findings to date include:
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