Reactive Filter Systems for Small Scale Wastewater Treatment – A literature review
The objective of this study was to outline via a literature review reactive filter systems for small scale wastewater treatment. Phosphorus and ammonium sorption were considered. Different reactive filter materials have been studied in a laboratory, though few in full-scale. The lightweigh clay aggregate product Filtralite P and Nordkalk Filtra P are the materials most used in full-scale applications and sorb phosphorus efficiently. Blast furnace slag and Polonite are other promising phosphorus sorbents, but require full-scale studies before they can be recommended. A reactive filter system needs at least a sludge separation unit, a pre-treatment step and a reactive filter. The pre-treatment step contributes to the BOD and nitrogen removal and decreases the clogging risk of the reactive filter unit. Locating the reactive filter material in a separate filter unit facilitates the replacement of exhausted material and the recovery of sorbed nutrients. Ammonium adsorbs efficiently to zeolites, but larger amounts of filter material are needed for ammonium adsorption compared to corresponding systems for phosphorus sorption due to higher wastewater concentrations. Further research is needed regarding the longevity of the sorbents, influence of resting periods, leakage of sulphuric compounds and heavy metals, desorption, risks of using sorbents as fertilisers and system analyses.