Biological nitrification and denitrification of opto-electronic industrial wastewater.
Development and application of biological nutrient removal processes accelerated significantly over the past decade due to more stringent nutrients (nitrogen and phosphorus) discharge limits being imposed on wastewater treatment plants. The opto-electronic industry has developed very fast over the past decade in the world. The wastewater often contains a significant quantity of organic nitrogen compounds and has a ratio of over 95% in organic nitrogen (Org-N) to total nitrogen (T-N). In this study, a 2-stage Anoxic/Aerobic pre-denitrification process was established and the efficiency of wastewater treatment was evaluated. Wastewater from an actual LCD-plant was obtained as the sample for looking into the feasibility of opto-electronic industrial wastewater treatment. Hydraulic retention time (HRT) and mixed liquor recycle rate (MLR) were controlled independently to distinguish between the effects of these two factors. Under suitable HRT and mixed liquor recycle ratio, effluents of NH4-N, NOx-N and COD can fall below 20 mg/l, 30 mg/l and 80 mg/l.
Treatment of chlorobenzene-contaminated groundwater in a pilot-scale constructed wetland
Abstract At industrial megasites worldwide, the natural seepage of contaminated groundwater from surface-near layers into rivers and river floodplains may give rise to serious environmental hazards. To prevent adverse effects on the environment, affordable and energy-efficient treatment methods for these sites are required. Large-scale constructed wetlands (CW) may represent a promising approach to protect river catchment areas. A pilot-scale horizontal subsurface flow CW planted with Phragmites australis and an unplanted reference plot were investigated for the removal of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DBC) and 1,2-dichlorobenzene (1,2-DCB) from polluted groundwater in Bitterfeld (Germany). At inflow concentrations of 20 mg L −1 MCB, 0.19 mg L −1 1,2-DCB and 0.25 mg L −1 1,4-DCB, the planted system showed high removals of MCB and 1,4-DCB already after 2 m of the flow path with averages of 48% MCB and 38% 1,4-DCB over all depths (71% MCB and 62% 1,4-DCB in the upper layer of the wetland). The unplanted wetland showed its highest mean removals only after 4 m of the flow path with 35% MCB and 32% 1,4-DCB. 1,2-DCB was not removed in either system. Oxygen limitation prevailed in both systems but concentrations were higher in the planted wetland with redox potentials of 65–90 mV (0–65 mV in the unplanted wetland). The presence and activity of aerobic MCB degraders in the wetland was shown via most probable number (MPN) determination and aerobic microcosm experiments. Since plants have a significant effect on chlorobenzene removal, constructed wetlands provide a high potential for the treatment of chlorobenzene-contaminated groundwater.
Single-sludge nitrogen removal: modeling and experimental results
basin which is maintained under anoxic conditions for denitri fication. The mixed liquor is then passed to the aerobic reactor for nitrification and residual organic carbon removal. Mixed liquor from the aerobic basin is recycled to the anoxic basin to provide nitrate for denitrification. Because of the interactions between various microbial species and substrates, and the recycle of mixed liquor, mathematical models that depict these systems can be rather complex. Several models with varying levels of complexity have been proposed in recent years.5"9 For design purposes, a highly sophisticated model, which accounts for every detail of the process, is hardly justified. The model should, however, be based on mechanistic principles so it can be extrapolated, and be capable of predicting performance with reasonable accuracy. The components of any mathematical model for the single sludge system consist of a set of equations that describe process kinetics, materials balance, and stoichiometry. Various equations have been used in the past for the individual processes of chem ical oxygen demand (COD) removal, nitrification, and denitri fication. The objective of this work is to examine the applicability of several of these alternative equations for the combined single sludge system. It also illustrates the derivation of some process parameters from experiments on continuous-flow single-sludge systems. The discussion here is limited to treatment systems for wastewater that contains carbonaceous organics (expressed as COD) and ammonia nitrogen. The concentrations of all nitrogen compounds are expressed in mg/L as N. Unless stated otherwise, nitrates or NO3 in this paper, mean total oxidized nitrogen or NOJ + NOJ.