Touki Takahashi
Phosphorus recovery from sewage with DHS reactor
Akiyoshi Ohashi
Phosphate recovery from sewage is desirable, because of phosphate resource deplesion. Conventional technology has some problems, e.g. cost of aeration and disposal of excess sludge. Since UASB+DHS system is less excess sludge and less motive aeration energy, and it attracts attention as future generation sewage treatment. But this system doesn't remove phosphate at all. As a result, UASB+DHS discharge contains low concentration phosphorus. Low concentration phosphorus is difficult to recover, and causes eutrophication problem.
So, we developed phosphate recovery system intended for municipal discharge (UASB+DHS discharge). The equipment is airtight DHS whose gas phase go over anaerobic and aerobic, and PAOs (Polyphosphate Accumulating Organisms) retains in the sponge. In aerobic phase, municipal discharge is supplied, and PAOs uptakes phosphorus and store in the body. In anaerobic phase, Organic wastewater is supplied, and PAOs uptake organic matter and release phosphorus from body into water. Therefore, organic wastewater becomes high phosphorus concentrated water, and phsphorus in municipal discharge is removed.
First, Plugflow reactor was set up as simulation of DHS. Substrate is synthetic municipal discharge, and acetate contains water. In case of collecting 5% of total effluent, pohosphorus concentraion was 58mgP/L (11 times as Inf.), phosphate recovery percentage was 58%.
Second, real sewage lacks VFAs which are PAOs's substrate. So VFAs is generated by Primary sludge acidogenic fermentation. As a result, 25% of total COD changed into VFAs, it was enough to supply VFA with PAOs.
Finally, we tried phosphorus remocovery with DHS using acidification primary liquid. The experimental condition is completely anaerobic-aerobic control. In case of collecting 5% of total effluent, pohosphorus concentraion is 31mgP/L (6 times as Inf.), phosphate recovery percentage is 61%.
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