Polyelectrolytes ability in reducing atrazine concentration in water: surface effects.

This paper reports on the direct ability of two positively charged organic polyelectrolytes (natural-based and synthetic) to reduce the atrazine concentration in water. The adsorption study was set up using multiple glass vessels with different polymer dosing levels followed by ultrafiltration with a 1 kDa membrane. The addition of polymers exhibited a capability in reducing the atrazine concentration up to a maximum of 60% in surface-to-volume ratio experiments. In the beginning, the theoretical L-type of the isotherm of Giles' classification was expected with an increase in the dosage of the polymer. However, in this study, the conventional type of isotherm was not observed. It was found that the adsorption of the cationic polymer on the negatively charged glass surface was necessary and influential for the removal of atrazine. Surface-to-volume ratio adsorption experiments were performed to elucidate the mechanisms and the polymer configuration. The glass surface area was determined to be a limiting parameter in the adsorption mechanism.

Use of flocculants for increasing permeate flux in anaerobic membrane bioreactors.

Biomass retention, required for high rate anaerobic wastewater treatment, can be accomplished coupling an anaerobic bioreactor with membrane filtration. However, low flux seems to be a common factor when operating anaerobic membrane bioreactors (AnMBRs). Modification of biomass properties may represent a strategy for improving membrane flux. The addition of flocculants was tested as a tool for flux increase. Six different products were tested in dead-end filtration experiments. Based on the results, two products were selected for cross-flow tests. The one presenting better performance (Nalco MPE50) was tested in a laboratory-scale continuous AnMBR. Results show that the flocculant was able to substantially increase flux. Indeed, the flux-increasing effect was observed for several weeks after flocculant addition. Therefore, the use of flocculants seems to be an interesting tool to cope with temporary increases in required flux.

Leaching and accumulation of trace elements in sulfate reducing granular sludge under concomitant thermophilic and low pH conditions.

The leaching and/or accumulation of trace elements in sulfate reducing granular sludge systems was investigated. Two thermophilic up-flow anaerobic sludge bed (UASB) reactors operated at pH 5 were fed with sucrose (4 gCOD l(reactor)(-1)d(-1)) and sulfate at different COD/SO(4)(2-) ratios. During the start-up of such acidogenic systems, an initial leaching of trace elements from the inoculum sludge occurred regardless of trace elements supplementation in the reactor influent. The granular sludge maintained the physical structure despite high Fe leaching. After start-up and nonetheless the acidic conditions, Co, Ni, Cu, Zn, Mo and Se were retained or accumulated by the sludge when added. Particularly, Ni and Co accumulated in the carbonates and exchangeable fractions ensuring potential bioavailability. Otherwise, the initial stock in the inoculum sludge sufficed to operate the process for nearly 1 year without supplementation of trace elements and no significant sludge wash-out occurred.

Sulfate reduction during the acidification of sucrose at pH 5 under thermophilic (55 degrees C) conditions. II: effect of sulfide and COD/SO(2-)(4) ratio.

This work studied the effect of the sulfide concentration and COD/SO(2-)(4) ratios (4 and 1) on sulfate reduction and acidification in a thermophilic (55 degrees C) UASB reactor fed with sucrose (4 g COD(l(reactor)d)(-1)) operated at a reactor mixed liquor pH controlled at 5 for a period of 301 days. When implementing N(2) stripping, sulfate reduction efficiencies up to 95%, corresponding to volumetric sulfate reduction rates of 0.87 and 4.2g (l(reactor)d)(-1) at the COD/SO(2-)(4) ratios of 4 and 1, respectively, were achieved. Sulfide was toxic to sulfate reduction at a total dissolved sulfide concentration of 100 mg l(-1). Acidification was always complete and acetate was the only form of substrate in the effluent at a COD/SO(2-)(4) ratio of 1. The sludge was well retained in the reactor and kept its granular shape throughout the reactor run.

Sulfate reduction during the acidification of sucrose at pH 5 under thermophilic (55 degrees C) conditions. I: effect of trace metals.

This work studied the effect of supplying trace metals (7.5 microM Fe and 0.5 microM Co, Ni, Mn, Zn, Cu, B, Se, Mo and W) on sulfate reduction and acidification in thermophilic (55 degrees C) UASB reactors fed with sucrose (4 g COD (l(reactor) d)(-1)) operated at a reactor mixed liquor pH controlled at 5. Trace metals were supplied to one UASB reactor and were omitted from the influent of a second UASB reactor. The influence of different trace metal concentrations was further assessed in batch tests performed with the sludge from the UASB reactor receiving no trace metals. The absence of trace metals in the influent did not affect the performance of the acidifying UASB reactor throughout the 305 day long reactor run, but supplying low concentrations of trace metals inhibited sulfate reduction.

Sulfate reduction at pH 4 during the thermophilic (55 degrees C) acidification of sucrose in UASB reactors.

Continuous sulfate reduction at pH 4.0 was demonstrated in a pH controlled thermophilic (55 degrees C) upflow anaerobic sludge bed reactor fed with sucrose at a COD/SO(4)(2-) ratio of 0.9 and an organic loading rate of 0.8 and 1.9 gCOD (l(reactor) d)(-1) for a period of 78 days. A nearly complete sulfate reduction efficiency was achieved throughout the reactor run, corresponding to sulfate removal rates of 0.91 and 1.92 g (l(reactor) d)(-1) at sulfate loading rates of 0.94 and 2 g (l(reactor) d)(-1), respectively, by keeping the sulfide concentration below 20 mg l(-1) due to stripping with nitrogen gas. Acidification was always complete and acetate was the only degradation intermediate left in the effluent, which did not exceed 180 mgCOD l(-1) in pseudo-stationary states. The sludge was well retained in the reactor and kept its granular form. Zn, Cu, Se, and Mo accumulated in the sludge, whereas Co, Ni, Fe, and Mn leached from the sludge, despite their continuous supply to the reactor via the influent. The bacterial diversity in the reactor sludge at the end of the reactor run was low and the culture was dominated by one acidifying species, resembling Thermoanaerobacterium sp., and one sulfate reducing species, resembling Desulfotomaculum sp.

Effect of COD/SO(4)(2-) ratio and sulfide on thermophilic (55 degrees C) sulfate reduction during the acidification of sucrose at pH 6.

This study investigated the effect of the COD/SO(4)(2-) ratio (4 and 1) and the sulfide concentration on the performance of thermophilic (55 degrees C) acidifying (pH 6) upflow anaerobic sludge bed reactors fed with sucrose at an organic loading rate of 4.5 g COD l(reactor)(-1)day(-1). Sulfate reduction efficiencies amounted to 65% and 25-35% for the COD/SO(4)(2-) ratios of 4 and 1, respectively. Acidification was complete at all the tested conditions and the electron flow was similar at the two COD/SO(4)(2-) ratios applied. The stepwise decrease of the sulfide concentrations in the reactors with a COD/SO(4)(2-) ratio of 1 by N(2) stripping caused an immediate stepwise increase in the sulfate reduction efficiencies, indicating a reversible inhibition by sulfide. The degree of reversibility was, however, affected by the growth conditions of the sludge. Acidifying sludge pre-grown at pH 6, at a COD/SO(4)(2-) ratio of 9 and exposed for 150 days to 115 mg l(-1) sulfide, showed a slower recovery from the sulfide inhibition than a freshly harvested sludge from a full scale treatment plant (pH 7 and COD/SO(4)(2-)=9.5) exposed for a 70 days to 200 mg l(-1) sulfide. In the latter case, the decrease of the sulfide concentration from 200 to 45 mg l(-1) (35 mg l(-1) undissociated sulfide) by N(2) stripping caused an immediate increase of the sulfate reduction efficiency from 35% to 96%.