Pesticide dissipation and microbial community changes in a biopurification system: influence of the rhizosphere.

The dissipation of atrazine, chlorpyrifos and iprodione in a biopurification system and changes in the microbial and some biological parameters influenced by the rhizosphere of Lolium perenne were studied in a column system packed with an organic biomixture. Three column depths were analyzed for residual pesticides, peroxidase, fluorescein diacetate activity and microbial communities. Fungal colonization was analyzed by confocal laser scanning microscopy to assess the extent of its proliferation in wheat straw. The L. perenne rhizosphere enhanced pesticide dissipation and negligible pesticide residues were detected at 20-30 cm column depth. Atrazine, chlorpyrifos and iprodione removal was 82, 89 and 74% respectively in the first 10 cm depth for columns with vegetal cover. The presence of L. perenne in contaminated columns stimulated peroxidase activity in all three column depth sections. Fluorescein diacetate activity decreased over time in all column sections with the highest values in biomixtures with vegetal cover. Microbial communities, analyzed by PCR-DGGE, were not affected by the pesticide mixture application, presenting high values of similarity (>65%) with and without vegetal cover. Microbial abundance of Actinobacteria varied according to treatment and no clear link was observed. However, bacterial abundance increased over time and was similar with and without vegetal cover. On the other hand, fungal abundance decreased in all sections of columns after 40 days, but an increase was observed in response to pesticide application. Fungal colonization and straw degradation during pesticide dissipation were verified by monitoring the lignin autofluorescence loss.

Chlorophenol degradation in soil columns inoculated with Anthracophyllum discolor immobilized on wheat grains.

The white-rot fungus Anthracophyllum discolor immobilized on wheat grains was evaluated for chlorophenol (2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) degradation in allophanic soil columns activated by acidification. Columns without inoculation were used as the control to evaluate the adsorption capacity of the soil columns. The chlorophenols were removed efficiently in soil columns by both adsorption and degradation processes. In inoculated soil columns, 2,4-dichlorophenol was highly degraded and this degradation is associated with a high production of manganese peroxidase. 2,4,6-trichlorophenol was degraded to a lesser extent compared with 2,4-dichlorophenol. Pentachlorophenol was first removed by adsorption and then through degradation by the fungus. Manganese peroxidase activity was lowest when the column was fed with pentachlorophenol and highest when the column was fed with 2,4-dichlorophenol. Laccase was also produced by the fungus but to a lesser degree.

Sliding mode control of dissolved oxygen in an integrated nitrogen removal process in a sequencing batch reactor (SBR).

This paper presents a sliding mode controller (SMC) for dissolved oxygen (DO) in an integrated nitrogen removal process carried out in a suspended biomass sequencing batch reactor (SBR). The SMC performance was compared against an auto-tuning PI controller with parameters adjusted at the beginning of the batch cycle. A method for cancelling the slow DO sensor dynamics was implemented by using a first order model of the sensor. Tests in a lab-scale reactor showed that the SMC offers a better disturbance rejection capability than the auto-tuning PI controller, furthermore providing reasonable performance in a wide range of operation. Thus, SMC becomes an effective robust nonlinear tool to the DO control in this process, being also simple from a computational point of view, allowing its implementation in devices such as industrial programmable logic controllers (PLCs).

Modes of operation and pH control as enhancement factors for partial nitrification with oxygen transport limitation.

Sequencing batch (SBR) and continuous operation modes were applied using different pH control strategies to enhance partial nitrification in a biofilm rotating disk reactor. The pH control strategies were supervisory control in the range of 7.5-8.6 and fixed pH at 7.5 and 8.5, at dissolved oxygen (DO) concentrations in the range of 0.6-5.0 mg O(2)/L. Supervisory pH control enabled operation at a free ammonia concentration inhibitory to the nitrite-oxidizing bacteria (NOB) and an optimum for the ammonia-oxidizing bacteria (AOB). The results indicate that both operation modes were simultaneously controlled by oxygen transport and micro-kinetics (influenced by pH and NH(3)). The SBR mode with supervisory pH control presented more stable partial nitrification-nitrite accumulation >80% for 249 days than continuous operation. Molecular analyses showed that the SBR operation with supervisory pH control at low DO concentrations contributed to the enrichment of the AOB (>95%) over the NOB (<5%) populations. Therefore, it can be stated that a suitable pH control strategy can act as an enhancement factor of partial nitrification even under oxygen-transport-limiting conditions.

Unhairing effluents treated by an activated sludge system.

Leather tannery effluents are a source of severe environmental impacts. In particular, the unhairing stage, belonging to beamhouse processes, generates a significantly toxic, alkaline wastewater with high concentrations of organic matter, sulphides, suspended solids and salts. The objective of this work was to evaluate the biodegradability and toxicity of diluted unhairing wastewater after being treated by an activated sludge (AS) system. The biomass activity of the AS was also evaluated. The AS system was fed for 180 days with diluted unhairing effluent. The operation strategy increased the organic load rate (OLR) from 0.23 to 2.98 g COD/l per day while the HRT was variable until operation day 113, when the HRT was near 1.1 days. Results show that when the organic load rate was lower than 2 g COD/l per day, the biological oxygen demand (BOD5) efficiency was 99%, whereas the chemical oxygen demand (COD) was around 80%. The reactor operation was stable until 2 g COD/l per day. For higher values, the system was less efficient (COD and BOD5 removal rate lower than 40%) and the relation of food/micro-organisms (F/M) was higher than 0.15. Biomass evaluations through oxygen utilisation coefficients show that the specific oxygen uptake rate (SOUR) decreased from 1.11 to 0.083 g O2/g MLVSS per day, in the same way the endogenous oxygen coefficient decreased from 0.77 to 0.058 per day. The reduction of biomass activity (measured as oxygen respiration) could be attributable to the inorganic compound content (ammonia and chloride) in the unhairing effluent. Also, the bioassays with Daphnia magna and Daphnia pulex showed that with these compounds, only between 24 and 31% of the toxicity of the aerobic-treated effluent can be removed. On the other hand, ultrafiltration (UF) analysis indicated that a COD fraction is recalcitrant to the aerobic treatment, principally those above 10,000 Da (around 55% of total unhairing influent COD).

Life cycle assessment as a tool for the environmental improvement of the tannery industry in developing countries.

A representative leather tannery industry in a Latin American developing country has been studied from an environmental point of view, including both technical and economic analysis. Life Cycle Analysis (LCA) methodology has been used for the quantification and evaluation of the impacts of the chromium tanning process as a basis to propose further improvement actions. Four main subsystems were considered: beamhouse, tanyard, retanning, and wood furnace. Damages to human health, ecosystem quality, and resources are mainly produced by the tanyard subsystem. The control and reduction of chromium and ammonia emissions are the critical points to be considered to improve the environmental performance of the process. Technologies available for improved management of chromium tanning were profoundly studied, and improvement actions related to optimized operational conditions and a high exhaustion chrome-tanning process were selected. These actions related to the implementation of internal procedures affected the economy of the process with savings ranging from US dollars 8.63 to US dollars 22.5 for the processing of 1 ton of wet salt hides, meanwhile the global environmental impact was reduced to 44-50%. Moreover, the treatment of wastewaters was considered in two scenarios. Primary treatment presented the largest reduction of the environmental impact of the tanning process, while no significant improvement for the evaluated impact categories was achieved when combining primary and secondary treatments.

Combined oxidative and biological treatment of separated streams of tannery wastewater.

Leather tanning effluents are a source of severe environmental impacts. In particular, the unhairing stage, belonging to the beamhouse processes, generates an alkaline wastewater with high concentrations of organic matter, sulphides, suspended solids, and salts, which shows significant toxicity. The objective of this work was to evaluate the biodegradation of this industrial wastewater by combined oxidative and biological treatments. An advanced oxidation process (AOP) with Fenton's reagent was used as batch pretreatment. The relationships of H2O2/Fe2+ and H2O2/COD were 9 and 4, respectively, reaching an organic matter removal of about 90%. Subsequently, the oxidised beamhouse effluent was fed to an activated sludge system, at increasing organic load rates (OLR), in the range of 0.4 to 1.6 g COD/L x day. The biological organic matter removal of the pre-treated wastewater ranged between 35% and 60% for COD, and from 60% to 70% for BOD. Therefore, sequential AOP pretreatment and biological aerobic treatment increased the overall COD removal up to 96%, compared to 60% without pretreatment. Bioassays with D. magna and D. pulex showed that this kind of treatment achieves only a partial toxicity removal of the tannery effluent.

Tannery wastewater characterization and toxicity effects on Daphnia spp.

Tannery wastewater contains large quantities of organic and inorganic compounds, including toxic substances such as sulfides and chromium salts. The evaluation of wastewater quality in Chile nowadays is based on chemical specific measurements and toxicity tests. The goal of this research was to characterize tannery wastewater and to relate its physical/chemical parameters with its acute toxicity effect on Daphnia pulex. To distinguish the most important toxic compounds, physical/chemical techniques were applied to a grab sample of a final effluent based on the Phase I toxicity identification evaluation (TIE) procedure. In addition, the toxicity of a beamhouse effluent after an activated sludge reactor treatment was investigated on Daphnia magna (introduced species) and D. pulex (native species). Effluent from different tannery processes (soaking, beamhouse, tanning and final) demonstrated high values of chemical organic demand (COD; 2840-27,600 mg L(-1)), chloride (1813-16,500 mg L(-1)), sulfate (230-35,200 mg L(-1)), and total solids (8600-87,100 mg L(-1)). All effluents showed extremely toxic effects on D. pulex, with 24-h mean lethal values (LC(50)) ranging from 0.36% to 3.61%. The Phase I TIE profile showed that toxicity was significantly reduced by air stripping, filtration, and a cationic exchange resin, with toxicity reductions ranging between 46% and 76%. The aerobically treated beamhouse effluent showed significantly less toxicity for both species (43%-74%). The chemical parameters demonstrated that the remaining toxicity of the treated beamhouse effluent was associated with its ammonia (120 mg N-NH(3) L(-1)) and chloride (11,300 mg Cl(-) L(-1)) contents.