Aerobic granulation utilizing fermented municipal wastewater under low pH and alkalinity conditions in a sequencing batch reactor.

The aim of this study was to achieve aerobic granulation utilizing fermented municipal wastewater under low pH, and alkalinity conditions. Stable granulation was achieved after a 166-day start-up period. Due to low influent strength, supplemental carbon addition, in the form of sucrose, was added to the feed storage tank on the 82nd day of start-up to facilitate granulation. This increased the system's organic loading rate from 1.43 ± 0.14 to 2.53 ± 0.18 kg COD/m(3)/d, and reduced the influent pH due to fermentation of the added sucrose. Although granulation was successful, the nutrient removal was limited. Removal rates at an influent pH of 6.23 ± 0.06 were 54.4% ± 8.3% for phosphorus, 21.9% ± 4.1% for ammonium, and 84.0% ± 3.0% for total chemical oxygen demand (COD). During the second phase of experimentation, increased amounts of sucrose were added to the feed, which resulted in increased volatile fatty acid concentrations and pH reduction to 5.62 ± 0.12 due to fermentation. Under further reduced pH conditions, phosphorus, ammonium, and total COD removal were found to be 58.9% ± 4.7%, 37.9% ± 4.7%, and 87.1% ± 0.9%, respectively. Settling volume indexes, SVI10 and SVI30, were found to be 148.8 ± 28.9 mL/g, for the influent pH of 6.23 ± 0.06, and 157.5 ± 40.6 mL/g, for the influent pH of 5.62 ± 0.12. This high SVI is indicative of the formation of lower-density granules in comparison to high-ash-content granules. The absence of denitrification-induced chemical phosphorus precipitation within the granule was likely a contributing factor to the low granule density observed in the system.

Long-term performance of side-stream deammonification in a continuous flow granular-activated sludge process for nitrogen removal from high ammonium wastewater.

An innovative granular sludge deammonification system was incorporated into a conventional-activated sludge process. The process incorporated an internal baffle in the bioreactor for continuous separation of granular biomass from flocculent biomass, which allowed for controlling the solids retention time of flocculent sludge. The process was evaluated for ammonium removal from municipal digested sludge dewatering centrate under various operating conditions lasting over 450 days. The process successfully removed, on average, 90% of the ammonium from centrate at various ammonium loading reaching 1.4 kg/m³d at 20 hours hydraulic retention time. Controlling the retention time of the flocculent biomass and maintaining low nitrite concentration were both found to be effective for nitrite oxidizing bacteria management, resulting in a low nitrate concentration (below 50 mg/L) over a wide range of flocculent biomass concentration in the bioreactor.

Investigation of chemical-free nutrient removal and recovery from CO2-rich wastewater.

The feasibility of a bench-scale system for removal and recovery of phosphorus (P) as struvite from CO2-rich wastewater was tested. A continuous 12 L reactor system combining a fluidized seedbed and aeration for pH increase was developed and tested using synthetic feed. For a 100 mL min(-1) influent rate, an aeration and recycle rate combination of 7 L min(-1) and 700 mL min(-1) was sufficient for increasing and maintaining the reactor pH from 6.7 to between 7.6 and 8.0. Significant P removal was achieved in 6 h runs without a seedbed (91-92%), while neither the struvite nor sand seedbeds improved P removal (91-96%). Struvite was recovered in all runs, with additional calcium (Ca) precipitation in the seedbed runs. Reactor operation was possible for an extended period of time, up to 46 h without any major adjustment during long-term run. The average P removal was 88%, and precipitate collected after 24 h was found to be mainly struvite, while the final precipitate had a Ca: total phosphorus molar ratio of 0.56 and also contained calcite. This study has demonstrated the technical feasibility of an aerated crystallization reactor system for chemical-free struvite removal and recovery from CO2-rich wastewater such as stored livestock manure.