No abstract

Anaerobic digestion of sludges favors the formation of struvite because ammonia, phosphate, and magnesium are solubilized by the digestion process. Struvite (MgNH4P04 · 6H20(s)) can cause problems through scale formation. This paper provides a rational method for predicting the optimum FeCl3 dose for preventing struvite formation during anaerobic digestion. Based on continuous flow anaerobic digestion experiments, the minimum dose to prevent struvite formation in the San Francisco Southeast Water Pollution Control Plant is 13.5 mM FeCl3/L or 100 kg FeCl3/ton total solids (TS). Approximately 68% of the total magnesium and total phosphorus present in the feed was available for chemical precipitation and the average ratio of soluble P04‐P removed to Fe added was 0.37. Additional iron demand was attributed to FeS(s) and FeC03(s) precipitation. Anaerobic sludge digestion batch studies showed similar soluble P04‐P removal efficiencies by FeCl3 and FeS04 dosing, indicating that Fe(III) is reduced readily to Fe(II) in anaerobic sludge digesters.

No abstract

Pilot-and bench-scale coliform inactivation tests with UV irradiation were used to show how suspended solids remaining in filtered secondary effluent affect the efficiency of the UV disinfection process. Observed kinetic inactivation rates decreased with increasing suspended particle sizes of 7 m or larger present in tertiary effluent. First-order inactivation rates estimated from collimated beam dose-response curves for discrete ranges of UV doses were substantially different, which should caution researchers not to compare inactivation data obtained with largely dissimilar UV doses or suspended particle distributions. A dose of approximately 800 J/m 2 was identified as the minimum dose that will consistently meet the California wastewater reclamation coliform criterion when applied to in-line filtration effluent. Water Environ. Res., 73, 233 (2001).

A direct comparison between parallel activated sludge and integrated fixed-film activated sludge (IFAS) processes was performed in this study because both treatments received the same primary effluent, although differences may still remain due to different return flow rates. Modern ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was applied to characterize the complexity of effluent organic matter (EfOM) and to evaluate both processes in their abilities to change the EfOM molecular composition. At different stages during the two processes a direct comparison of the performance and changes in molecular composition of the IFAS with those of the activated sludge was undertaken. Large differences in the molecular composition between both processes were only apparent in the early stage of the aeration cells and the first cell of the IFAS possibly due to the higher flow rate and a delay in aerobic bacterial degradation. Despite the double flow rate (0.263 m(3) s(-1)) in the IFAS reactors compared to the activated sludge, by the end of the treatment the EfOM composition of both processes were undistinguishable from each other. However, a much more complex EfOM was generated in both processes, suggesting that bacteria are responsible for an increase in molecular diversity in the effluent.

No abstract

Microfiltration and UV disinfection are two alternative technologies for water reclamation. The results of a pilot study combining these two processes are presented. In addition to producing filtrate turbidities averaging 0.06 nephelometric turbidity units, microfiltration was an effective barrier to pathogens, demonstrating average log reductions of 4.5 for total coliforms and 2.9 for MS2 bacteriophage. Ultraviolet disinfection following microfiltration reliably met the California Wastewater Reclamation Criteria (Title 22) total coliform standard of 2.2 colony‐forming units/l00 mL at a UV dose of 450 J/m2. The MS2 bacteriophage standard, which requires a 5‐log reduction, was achieved by microfiltration and a UV dose of 880 J/m2. A model of the kinetics of inactivation of MS2 bacteriophage was used in further analysis of disinfection data. The model indicated that considerable backmixing occurred in the pilot UV disinfection unit, and observed UV doses could be reduced with improved hydraulics.

This study investigated the fate of nitrogen species, especially organic nitrogen, along the mainstream wastewater treatment processes in four biological nutrient removal (BNR) wastewater treatment plants (WWTPs). It was found that the dissolved organic nitrogen (DON) fraction was as high as 47% of soluble nitrogen (SN) in the low‐SN effluent plant, which limited the plant's capability to remove nitrogen to very low levels. A lower DON fraction was observed in high‐SN effluent plants. Effluent DON concentrations from the four plants ranged from 0.5 to 2 mg N/L and did not vary significantly, even though there was a large variation in the influent organic nitrogen concentrations. Size fractionation of organic nitrogen by serial filtration through 1.2‐, 0.45‐, and 0.22‐µm pore‐sized membrane filters and the flocculation‐and‐filtration with zinc sulfate (ZnSO4) method was investigated. The maximum colloidal organic nitrogen (CON) fractions found were 68 and 45% in the primary effluent and final effluent, respectively. The experimental results showed that effluents after filtration through the 0.45‐µm pore‐sized filter contain significant colloidal fractions; hence, the constituents, including organic nitrogen, are not truly dissolved. A high CON fraction was observed in wastewater influents and was less significant in effluents. The flocculation and filtration method removed the colloidal fraction; therefore, the true DON fraction can be determined.