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Pesticide-producing factories generate highly polluting wastewaters containing toxic and hazardous compounds which should be reduced to acceptable levels before discharge. In this study, a chemical industry wastewater was treated in a pre-denitrification moving-bed biofilm reactor system subjected to an increasing internal mixed liquor recycle ratio from 2 to 4. Although the influent wastewater characteristics substantially varied over time, the removal of chemical oxygen demand (COD) and dissolved organic carbon was quite stable and mostly higher than 90%. The highest fraction of the incoming organic matter was removed anoxically, favouring a low COD/N environment in the subsequent aerobic nitrifying tank and thus ensuring stable ammonium removal (90-95%). However, during pH and salt shock periods, nitrifiers were severely inhibited but gradually restored their full nitrifying capability as non-stressing conditions were reestablished. Besides promoting an increase in the maximum nitrification potential of the aerobic attached biomass from 0.34 to 0.63 mg [Formula: see text], the increase in the internal recycle ratio was accompanied by an increase in nitrogen removal (60-78%) and maximum specific denitrification rate (2.7-3.3 mg NOx(-)--N). Total polysaccharides (PS) and protein (PT) concentrations of attached biomass were observed to be directly influenced by the influent organic loading rate, while the PS/PT ratio mainly ranged from 0.3 to 0.5. Results of Microtox tests showed that no toxicity was found in the effluent of both the anoxic and aerobic reactors, indicating that the biological process was effective in removing residual substances which might adversely affect the receiving waters' ecosystem.

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The treatment of a chemical industry wastewater with the goal of reuse was evaluated in a three-step process. First, the industrial waste stream underwent biological treatment in a two-stage moving-bed biofilm reactor (MBBR) system, which allowed achieving average effluent chemical oxygen demand (COD), dissolved organic carbon (DOC), ammonium, total nitrogen (TN), and total suspended solids (TSS) concentrations of 45.5, 27.2, 1.0, 34.2, and 210 mg/L, respectively. Salt and TSS concentrations after the MBBR process were still not compatible with the requirements for effluent reuse and the silt density index (SDI 15 ) was found to be > 6.5, making a direct reverse osmosis (RO) application impractical. By employing microfiltration (MF) downstream of the biological treatment, no salt removal was observed, but the SDI 15 was reduced to around 2, enabling final RO application. Long-term RO experiments conducted at different pressures (1.5-3.0 MPa) showed that biofouling became more severe under higher pressures, leading to the enhancement of the permeate flux drop. Rejection of DOC, TN, and salt by RO corresponded to 97.8 %, 89 %, and 99 %, respectively. The combined MBBR/MF/RO process allowed the production of a highquality effluent appropriate for direct reuse in the industry as feed water in cooling towers, steam boilers, and general industrial process activities. This article is protected by copyright.All rights reserved