Robert A. Rapaport

An improved model for predicting the fate of consumer product chemicals in wastewater treatment plants

Abstract The WW-TREAT model was developed to predict the fate of consumer product chemicals in primary and activated sludge wastewater treatment plants using independently determined values for the distribution coefficient between sludge solids and liquid, Henrys law constant and biodegradation rate constants. The major difference between this model and previous models is that it assumes the total chemical, not just the dissolved chemical, is available for biodegradation and that sorption to sludge solids increases the time that a chemical is available for biodegradation. The model was validated with monitoring data for four chemicals which possess sorption and biodegradation characteristics that span the range typical of the broader class of consumer product chemicals. Sensitivity analysis revealed that the most important parameters were the plant operating parameter, sludge/solids retention time and the chemical specific parameters, distribution coefficient and biodegradation rate constants. The sludge/solids retention time had its greatest effect when it was less than 9 days and the distribution coefficient had its greatest effect when it was between 100 and 3000 l/kg. The model predicted removal in primary and activated sludge wastewater treatment plants within 5%. Thus, the model can be used as a valuable tool for predicting the fate of consumer product chemicals.

Environmental fate and effects of DEEDMAC : a new rapidly biodegradable cationic surfactant for use in fabric softeners

This paper introduces the environmental safety database for a new fabric softening cationic surfactant, the di-(tallow fatty acid) ester of di-2-hydroxyethyl dimethyl ammonium chloride, DEEDMAC >Diethyl Ester Dimethyl Ammonium Chloride). The physiochemical properties of DEEDMAC are similar to those for ditallow dimethyl ammonium chloride (DTDMAC), the major cationic surfactant used in fabric softener formulations world-wide for over thirty years. Importantly, however, DEEDMAC differs structurally from DTDMAC by the inclusion of two weak ester linkages between the ethyl and tallow chains. These ester linkages allow DEEDMAC to be rapidly and completely biodegraded in standard laboratory screening tests and a range of environmental compartments. including raw sewage, activated sludge, anaerobic digestor sludge, sludge amended soil, and river waters. Removal of DEEDMAC during sewage treatment is greater than 99%, as determined by computer model predictions and confirmed by laboratory simulation testing (OECD Continuous Activated Sludge confirmatory test). Using estimated tonnages, per capita waste water flows, incidences of sewage treatment for individual countries, measured removal rates, and validated computer models, maximum river water and soil concentrations of DEEDMAC have been estimated for representative usage scenarios. Based upon these maximum predicted environmental concentrations, acute and chronic toxicity testing offish, invertebrates and algae, predicted aquatic safety factors range from 272 to > 1000. Predicted steady state terrestrial safety factors are > 1000, based on EC50 values to earthworms and plants >50 mg/kg. The environmental safety database developed for DEEDMAC indicates that this cationic surfactant is rapidly and completely biodegraded, will be highly removed during sewage treatment. has an ecotoxicity profile similar to broadly used anionic and nonionic surfactants, and is environmentally safe at intended maximum usage volumes.

A novel bioreactor simulating composting of municipal solid waste

Abstract A bioreactor (19L) was developed to simulate municipal solid waste composting. The purpose of the reactor was to provide a test system for evaluating physical changes in newly developed materials that may enter the portion of the waste stream being composted. To minimize variation in feed stock, the bioreactor utilized a defined waste mixture consisting of rabbit chow with alfalfa and shredded newspaper inoculated with a 1:1:1 mixture of leaf compost, garden soil, and cow manure. During the first 24 h, the mixture self-heated from 37°C. Scanning electron micrographs showed that populations of Bacillus-like bacteria dominated the composting mass. Enzyme activity, total bacterial CFU per gram dry weight, acridine orange direct microscopic counts of bacteria, and cellulose mineralization rates increased initially and remained high throughout a 28 day incubation period. After 28 days, volatile solids had decreased from 88 to 77% of the dry weight, and carbon nitrogen ratios had decreased from 35 to 14. It was concluded that under moist, aerobic conditions, simulated solid waste can undergo changes comparable to those reported for municipal solid waste in full-scale composting systems. Thus, the reactor is appropriate for testing the fate of potentially compostable materials.

An environmental risk assessment for DTDMAC in the Netherlands

The environmental safety of the cationic surfactant, ditallow dimethyl ammonium chloride (DTDMAC), has been determined from usage rates and fate data from The Netherlands and standard, well accepted assessment techniques. An environmental concentration model was developed using DTDMAC tonnages for 1990, actual per capita waste flow, and measured removal rates in wastewater treatment plants. This model incorporated a state of the art dilution model, instream removal and background DTDMAC concentrations. Based on this model, the 90th percentile river concentration of DTDMAC below wastewater treatment plant outfalls was estimated as 0.021 mg/L (i.e., 90% of Dutch surface waters receiving wastewater effluents have environmental concentrations less than 0.021 mg/L). This estimated concentration agrees well with the maximum measured DTDMAC concentrations in Dutch surface waters. Toxicity values for the risk assessment were derived from a study which used an environmentally relevant dosing system (i.e., effluent from an activated sludge treatment system) to measure commercial DTDMAC toxicity. Based on chronic toxicity data for Ceriodaphniadubia and Selenastrumcapricornutum from this study, a no effect level of 4.53 mg/L was determined for use in the risk assessment. Thus, the DTDMAC safety factor for aquatic organisms is 215 (4.53/0.021). It is concluded that DTDMAC poses a low risk to aquatic life based on testing of sensitive species and environmental concentrations predicted by state-of-the-art assessment methods.

First validation of a model for the adsorption of linear alkylbenzenesulfonate (LAS) to sediment and comparison to chronic effects data

Abstract A model for surfactant sorption proposed by Di Toro et al. (1) is compared to riverine monitoring data for linear alkylbenzenesulfonate (LAS). The model predicts sorption distribution coefficients (Kd) to within one order of magnitude of measured field values. Field determined values of Kd range from 11 to >24 for sediment/interstitial waters, and from 1000 to >5700 for suspended solids/overlying waters. The model provides an interpretive framework for evaluating the safety of monitored LAS concentrations to aquatic organisms, by enabling prediction of free concentrations of LAS in sediment interstitial waters.