No abstract

No abstract

No abstract

In this work, the biodegradation of by-products formed by ozonation of the azo dye Reactive Red 239 was evaluated using two MBBRs in series. Two ozone dosages were applied and low carbon removals and increasing ozone consumption observed after discoloration show the formation of oxidation resistant by-products. Five by-products were identified by GC/MS. High COD removal (90%) was observed in the biological process. However, nitrification inhibition was observed with ammonium removal of only 40%. This inhibition was probably caused by 4-amino-6-chloro-1,3,5-triazine-2-ol, which passed unscathed in the MBBRs. The nitrifying activity of the biofilm was restored when the MBBRs in series were fed with synthetic effluent (without by-products), proving the inhibition of nitrifying bacteria by ozonation by-products. The association of ozonation with the biological process was efficient in RR 239 color removal and degradation of some by-products. Higher ozone dosages are required for triazine oxidation, which probably inhibited nitrification in the MBBRs in series. The importance of identifying by-products formed by ozonation and their metabolization or not in a biological process is clear. In addition to partially inhibiting nitrification, special attention should be paid to chemicals that pass undegraded through a biological process and can be released into receiving bodies.

No abstract

No abstract

No abstract

In this study, removal of organic matter and nitrogen from a cattle slaughterhouse wastewater was investigated in a two‐stage anoxic–aerobic biological system, followed by UV‐C disinfection. Ecotoxicity of the raw, biotreated, and disinfected wastewater against the microalgae Scenedesmus sp. was evaluated in short‐term tests, while the potential of the microalgae as a nutrient removal step was addressed in long‐term experiments. Throughout 5 operational phases, the biological system was subjected to gradual reduction of the hydraulic retention time (8–1.5 day), increasing the organic (0.21–1.11 kgCOD·m−3·day−1) and nitrogen (0.05–0.28 kgN·m−3· day−1) loading rates. COD and total ammoniacal nitrogen (TAN) removal ranged within 83%–97% and 83%–99%, respectively. While providing alkalinity source, effluent TAN concentrations were below 5 mg·L‐1. Nitrate was the main nitrification product, while nitrite levels remained low (<1 mgN·L‐1). Upon supplementation of external COD as ethanol, total nitrogen removal reached up to 90% at the highest load (0.28 kgN·m−3·day−1). After UV‐C treatment, 3‐log reduction of total coliforms was attained. The 96‐hr ecotoxicity tests showed that all non‐diluted samples tested (raw, biologically treated and UV‐C irradiated wastewater) were toxic to microalgae. Nevertheless, these organisms were able to acclimate and grow under the imposed conditions, allowing to achieve nitrogen and phosphorous removal up to 99.1% and 43.0%, respectively. Practitioner points The treatment of a slaughterhouse wastewater in an anoxic–aerobic biological system followed by a UV‐C disinfection step was assessed. The pre‐denitrification system showed efficient simultaneous removal of organic matter and nitrogen from the wastewater under increasing applied loads. UV‐C disinfection worked effectively in reducing coliforms from the biotreated effluent, boosting the performance of microalgae on nutrients removal. Despite the toxicity to microalgae, they were capable to acclimate to the aqueous matrices tested, reducing efficiently the nutrients content. The combined stages of treatment presented great capacity for depleting up to 97% COD, 99% nitrogen, and 43% phosphorous.