Laboratory measurements of the volatilization of PCBs from amended dredged material

Since 1997, over 6 million cubic meters of material dredged from the navigation channels of NY/NJ Harbor has been amended with Portland cement and then used as fill and capping material at landfill and brownfield sites in New Jersey, New York, and Pennsylvania. Previous studies have determined that polychlorinated biphenyls (PCBs) will volatilize from this material as it dries. In the present study, time constants for the decay of the volatilization rate were determined taking into account the degree of stabilization. The experiments were conducted in a laminar flow flux chamber in which air was drawn past the dredged material and then through a polyurethane foam (PUF), sample matrix. The concentration of PCBs on the PUF found at various time increments at the downstream end of the chamber was compared to that found for the same time increments in a PUF installed in an air sampler at the upstream end of the chamber in order to calculate the flux. The time constant determined for raw dredged material was about 4 times greater than material stabilized with 8% Portland cement. The average time constants for the decay of flux rates from raw dredged material were 56, 67, and 60h for the di-, tri-, and tetra-chlorinated homologues, respectively. These times decreased with increasing proportion of Portland cement in the mixture. When stabilized with 8% Portland cement, the average time constants were 14, 13, and 19h, respectively. The effects of temperature on PCB flux rate were also investigated. The results suggest that a 3 degrees C temperature increase will more than double the flux rate.

Nutrient recovery and biodegradation of inedible tomato plant residues by activated sludge cultures and Phanerochaete chrysosporium

The biodegradation of inedible biomass and the recovery of nutrients from hydroponically grown tomato plant material were investigated under various growth conditions of activated sludge and the fungus Phanerochaete chrysosporium. The experiments were carried out in shaker flasks at three incubation temperatures (25 degrees C, 40 degrees C, and 60 degrees C for the activated sludge and 25 degrees C, 40 degrees C, and 50 degrees C for the fungi) with heat-pretreated samples at 150 degrees C for 30 min, and without pretreatment of the inedible residues. Under the experimental conditions tested, both cultures exhibited similar performance in terms of solids reduction and nutrient recovery. Solids reduction as high as 70% was obtained in both systems. Most of the solids degradation occurred the first 16 days of incubation. Cellulose degradation reached about 90% but no significant reduction in the solids lignin content was observed. Recovery of nitrogen (as NO2-N and NO3-N) and other micronutrients was sufficiently high and was accompanied by an average 70% reduction in COD, indicating that the final effluent is suitable for hydroponic plant growth. Incubation temperature had a minimal effect on solids degradation but appeared to influence the leachability of certain nutrients.

Redox transformations of arsenic and iron in water treatment sludge during aging and TCLP extraction

Laboratory experiments and modeling studies were performed to investigate the redox transformations of arsenic and iron in water treatment sludge during aging, and to evaluate the impact of those transformations on the leachability of arsenic determined with the U.S. EPA toxicity characteristic leaching procedure (TCLP). When the backwash suspension samples collected from a California surface water treatment plant were aged in closed containers for a few weeks, soluble arsenic increased from less than 5 microg/L to as high as 700 microg/L and then decreased dramatically because of biotic reduction of arsenate [As(V)], ferric oxyhydroxide, and sulfate. The experimental results and the thermodynamic models showed that arsenic mobility can be divided into three redox zones: (a) an adsorption zone at pe > 0, which is characterized by strong adsorption of As(V) on ferric oxyhydroxide; (b) a mobilization (transition) zone at -4.0 < pe < 0, where arsenic is released because of reduction of ferric oxyhydroxide to ferrous iron and As(V) to arsenite [As(III)]; and (c) a reductive fixation zone at pe < -4.0, where arsenic is immobilized by pyrite and other reduced solid phases. The TCLP substantially underestimated the leachability of arsenic in the anoxic sludge collected from sludge ponds because of the oxidation of Fe(II) and As(III) by oxygen. The leaching test should be performed in zero-headspace vessels or under nitrogen to minimize the transformations of the redox-sensitive chemical species.

Treatment of arsenic in Bangladesh well water using a household co-precipitation and filtration system

Laboratory and field tests were conducted to evaluate the effectiveness of a household filtration process and investigate the effects of phosphate and silicate on the removal of arsenic from Bangladesh groundwater by ferric hydroxides. Fe/As ratios of greater than 40 (mg/mg) were required to reduce arsenic to less than 50 microg/L in Bangladesh well water due to the presence of elevated phosphate and silicate concentrations. The household filtration process included co-precipitation of arsenic by adding a packet (approximately 2 g) of ferric and hypochlorite salts to 20 L of well water and subsequent filtration of the water through a bucket sand filter. A field demonstration study was performed to test the treatment system in seven households in Bangladesh in March and April 2000. Experimental results obtained from the participating families proved that the household treatment process removed arsenic from approximately 300 microg/L in the well water to less than 50 microg/L. The participating families liked this simple and affordable process and used it to prepare clean water for drinking and cooking. A larger scale field test is currently underway.