Date of Award

12-2012

Degree Name

MS in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

Advisor

Tryg Lundquist

Abstract

Bioflocculation of Wastewater Treatment Pond Suspended Solids

Louis Lefebvre

Wastewater treatment lagoons and high rate algae ponds (HRAPs) can provide cost effective wastewater treatment, but they commonly have high effluent concentrations of total suspended solids (TSS). In this thesis algae pond effluent was treated in a beaker testing apparatus (mixed and aerated) with various mixtures of activated sludge and primary effluent simulating differing activated sludge aeration basin compositions then was allowed to settle to assess settleability. Conventionally, microalgal suspended solids are removed by chemical coagulation followed by separation methods that often have a high cost relative to the low cost lagoon or HRAP system where the solids were produced. This separation step is often cost prohibitive or operationally complex for municipalities or too energy intensive for application in algae biofuels production. This research investigates using a small amount of activated sludge material to promote bioflocculation of algae in pond effluent. It was hoped that the findings may demonstrate a path for municipalities to keep their lagoons, while increasing capacity and improving treatment without excessive cost or complexity. Experiments were conducted on microalgae samples from a pilot-scale HRAP and activated sludge and primary effluent samples from a local municipal wastewater plant. The samples were placed in a mixing apparatus and allowed to settle for a given period of time, after which TSS was analyzed for settleability. The experiments investigated the effect of various lab-scale activated sludge reactor operational schemes by varying the volumes (and masses) of activated sludge, algae-rich water, and activated sludge in the beaker. Results in the sorption test (tests with only activated sludge and algae-rich water) demonstrated algae pond effluent treated with activated sludge concentrations of 3000 mg/L or greater produced final effluent TSS concentrations near discharge requirements (40-50 mg/L) with only 30 minutes of settling and without addition of primary effluent. However, such high activated sludge concentrations are not feasible at full scale. Furthermore, beakers with activated sludge concentrations greater than 3000 mg/L reduced TSS concentrations by more than 150 mg/L with only 30 minutes of settling and without addition of primary effluent. Results in the aerobic beaker tests (tests with primary effluent, activated sludge, and algae-rich water) showed greater than 200 mg/L TSS removal and final effluent TSS concentration less than 30 mg/L was achieved using activated sludge to primary effluent volumetric ratios of 1:1 and greater which corresponded to activated sludge concentrations of 730 mg/L and greater. Activated sludge concentrations of 730 mg/L may not be feasible at full scale. This report shows that a PETRO-like process is effective in lowering wastewater pond suspended solids, however not to typical discharge standards.

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