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Methanogenic granular sludge and wastewater fermented sludge were used as inocula for batch tests of anaerobic bioremediation of chlorinated pesticide contaminated soil. Results obtained for both types of biomass were similar: 80 to over 90% of gamma -hexachlorocyclohexane (gamma-HCH), 1,1,1-trichloro-2,2-bis-(4-methoxyphenyl)ethane (methoxychlor) and 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)ethane (DDT) removed in 4-6 weeks. Residual fractions of these pesticides persisted till the end of the 16-week experiment. DDT was degraded through 1,1-dichloro-2,2-bis-(4-chlorophenyl)ethane (DDD). Accumulation of this product corresponded stoichiometrically only to 34-53% of removed DDT, supposedly due to its further transformations, finally resulting in formation of detected 4,4'-dichlorobenzophenone (DBP). Addition of 0.5 mM Tween 80 nonionic surfactant resulted in about a twofold decrease of gamma -HCH and methoxychlor residual concentrations, as well as considerably lower DDD accumulation (7-29%) and higher DBP production. However, 1.25 mM dose of this surfactant applied together with granular sludge brought DDD levels back to that observed for treatments with the sludge alone, also impairing DBP formation.

Anaerobic biodegradation of DDT in field-polluted soil was investigated in relation to Tween 80 surfactant dose and initial pollution level. Experiments were carried out as lab-scale tests with flooded soil, inoculated with granular sludge. Higher surfactant doses decreased DDT residual concentration and also reduced DDD metabolite accumulation. However, doses higher than optimum caused DDD production to increase again. Results were also better for lower initial contamination levels-DDD accumulation was smaller whereas formation of terminal metabolite DBP was higher, indicating an enhancement of DDT transformation. Tests with pure compounds spiked in clean soil demonstrated that DDD is degraded slowly. Results point to three possible parallel pathways of anaerobic DDT transformation, not, as commonly reported, only one starting with dechlorination to DDD.

Bioremediation is intensively studied today as a treatment method for soil contaminated with chlorinated pesticides, chemicals counted among persistent organic pollutants. In the presented work, results of desorption kinetics study using consecutive Tenax TA solid phase extraction (SPE) were tested as predictors of 3‐wk anaerobic soil bioremediation effectiveness for chlorinated pesticides γ‐HCH, DDT, and methoxychlor. Field‐contaminated samples were used in these experiments, and conditions of bioremediation tests were based on previous research. Amounts of pesticides removed during bioremediation (43–98% of initial concentrations) were in most cases much larger (average ratio 1.37) than rapidly desorbing fractions estimated in SPE using two‐compartment model of desorption kinetics. The scatter of results was also considerable (standard deviation 0.45). However, there was a statistically significant correlation between amounts removed and rapidly desorbing fractions (R2 = 0.64), indicating a relationship between degradability and desorbability. Nonetheless, determination of rapidly desorbing fractions was considered rather a poor indicator of soil bioremediation efficiency for chlorinated pesticides. The total amounts of pesticides desorbed by Tenax in 72 h performed better in this respect (R2 = 0.73, fraction removed/desorbed = 1.10 ± 0.20, average ± standard deviation). Disappearance of DDT during bioremediation was accompanied by DDD formation but this was considerably lower than results expected from stoichiometry.

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Suitability of various substrates for anaerobic biodegradation of DDT in contaminated soil was tested in lab-scale tests with granular sludge inoculation. Use of carbohydrate-based substances such as starch, sucrose, molasses and whey resulted in acidification, which in extreme cases inhibited DDT removal. A large amount of phosphate buffer prevented pH drop for starch, but not for sucrose. Better results were obtained with calcium carbonate as a buffering agent, which also had little effect on soil salinity. Very good effectiveness of biodegradation was achieved using sodium lactate which, however, caused alkalinisation of the soil, perhaps due to accumulation of sodium carbonate. Alkalinisation did not occur when calcium lactate was used instead. Experiments also demonstrated that Tween 80 surfactant could be successfully used as a substrate, without experiencing problems with pH control.

Abstract:The paper presents the results of experiments on ecological toxicity assessment performed for 12 soil samples collected at 3 obsolete pesticide "tombs" in Poland, before their final disposal. Bioavailability of the main pollutants: p,p'-DDT, lindane and methoxychlor was assessed for selected samples by consecutive solid phase extraction using a Tenax TA sorbent. Several toxicity bioassays were also carried out, including: reducers (Microtox Soild Phase), producers (Phytotox) and consumers (tests of avoidance, acute toxicity and reproduction with use of the earthworm Eisenia foetida). Data from toxicity tests were discussed against the results of the chemical analysis of a wide range of pesticides determined by GC-ECD and GC-NPD. This part of the study enabled the evaluation of the applicability of the aforementioned bioassays in the assessment of pesticide soil pollution. Results of toxicity tests showed a slight to severe impairment of habitat function for all of the contaminated samples, which was only partially reflected by the analytical data. The most sensitive biotest was earthworm reproduction, followed by Phytotox and earthworm acute toxicity. Earthworm avoidance and Microtox tests were found to be of rather limited usability.

One of the critical technological parameter in operation of aerated submerged fixedbed biofilm reactor (ASFBBR) is the control over process of biofilm detachment. Both, an excessive growth of biomass with its accumulation in the bioreactor and an exceeded biofilm detachment rate, cause serious operational and technological problems. The studies presented in this paper demonstrate that in an ASFBBR reactor with a PVC bed carrier media, an effective way to maintain a proper shear stress acting on the biofilm and causing its detachment could be an internal recirculation of wastewater instead of backwashing with wastewater or air flushing. In case of polishing of oil-refinery wastewater with average COD loading rate equal to 9 g COD/(m 2 day), the minimum value of the hydraulic loading rate in such reactor is 1.9 m 3 /(m 2 h), at which there was no excessive growth of biofilms. Despite a significant decrease of the biofilms thickness and amount of biomass in the reactor, there was no significant decline in the efficiency of pollutant removal from oil-refinery wastewater, which made it possible to obtain the quality of effluent at the outlet of the bioreactor significantly below the water permits and standards.