No abstract

No abstract

No abstract

Although aluminum-and iron-based chemicals have been broadly used as the two most common types of coagulants for wastewater treatment, their impacts on the performance of downstream sludge management can be quite different and have not been well understood. This work reviewed and analyzed their similarities and differences in the context of the anaerobic digestion performance, dewaterability of digested sludge, and odor emission from dewatered biosolids. In short, iron-based coagulants tend to show less negative impact than aluminum-based coagulants. This can be attributed to the reduction of ferric to ferrous ions in the course of anaerobic digestion, which leads to a suite of changes in protein bioavailability, alkalinity and hydrogen sulfide levels, and in turn the sludge dewaterability and odor potential. Whether these observations still hold true in the context of thermally hydrolyzed sludge management remains to be studied. Practitioner Points• The impacts of aluminum-/iron-based coagulant addition on municipal sludge anaerobic digestibility, dewaterability, and odor emission are reviewed.• Iron-based coagulants show less negative impact on the sludge digestibility than aluminum-based coagulants.• Conclusions may aid practitioners in selecting coagulants in practice and better understanding the mechanisms behind the phenomena.

Washington, District of Columbia, installed activated carbon‐based lead mitigation filters on all water fountains/sinks in break rooms, classrooms, and health suites located in public elementary schools. To investigate the impact of these point‐of‐use filters, 12 water fountains/taps with various filter ages, with and without sediment prefilters, spread across four schools were monitored weekly from July to December 2017, along with two unfiltered sources per school (n = 8). Within the first 100 days postinstallation, filtrate from filters in schools with high influent monochloramine and no prefilter temporarily increased nitrite concentrations, with concentrations of some filters exceeding 0.4 mg/L N. Subsequent decreases in filtrate nitrite for these filters coincided with increases in live cell counts. Microbial community “fingerprints” were determined with flow cytometry. Filtered and unfiltered water fingerprints differed, indicating selective microbial growth on, and release from, the filters into the filtrate.

Free ammonia (FA) inhibition has been taken advantage as a strategy to suppress the growth of nitrite‐oxidizing bacteria (NOB) in aerobic granules stabilized in a continuous upflow airlift reactor to achieve partial nitritation. However, after nearly 18 months of continuous exposure of aerobic granules to FA in the reactor, the FA inhibition of NOB was proven ineffective, and the partial nitritation gradually shifted to partial nitrification even though the long‐term granule structural stability remained excellent under the continuous‐flow mode. The extent of NOB resistance to FA inhibition was quantified based on the kinetic response of NOB to various FA concentrations in the form of an uncompetitive inhibition coefficient. It was confirmed that the NOB immobilized in larger granules under longer term exposure to FA tend to become more resistant to FA. Thereby, it was concluded that NOB can develop strong resistance to FA after continuous exposure, and thus, FA inhibition is not a reliable strategy to achieve partial nitritation in mainstream wastewater treatment. Practitioner points Nitrifying aerobic granules can remain structurally stable in continuous‐flow bioreactors. NOB developed free ammonia resistance after 6‐month continuous exposure. Larger aerobic granules tended to develop stronger free ammonia resistance. Free ammonia inhibition is not a reliable strategy for mainstream anammox.

Cerium chloride (CeCl3), being a superior orthophosphate (OP) precipitant, was found to be able to significantly improve sludge dewaterability in terms of sludge cake dryness and capillary suction time. In order to offer insights into the mechanism behind OP removal associated dewaterability improvement, the change in sludge specific resistance to filtration (SRF), compressibility (K), and bound water contents (Ub) in response to CeCl3 and CePO4 addition at the two cationic polymer doses was mathematically simulated. Results showed that 29.8 g/kg dry solid CePO4 addition was able to decrease the SRF by 52%, decrease the Ub by 42%, and reduce the K by 18%. Importantly, CeCl3 addition of equal cerium molarity showed even higher SRF and Ub reductions by 67% and 54%, respectively, but the same K reduction. A new theory depicting how the OP has outcompeted negatively charged sludge particles for cationic polymers is put forward in this study to interpret the effect of OP removal on sludge dewaterability improvement. Practitioner points Efficient orthophosphate (OP) removal and sludge dewaterability improvement were achieved with CeCl3 addition. Both CePO4 precipitate and OP removal contributed to the improved dewaterability. Competition between OP and sludge particles for cationic polymers was explained.

No abstract