Influence of process parameters on anaerobic biodegradation of DDT in contaminated soil preliminary lab-scale study. Part I. Surfactant and initial contamination level

Abstract

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.

Influence of process parameters on anaerobic biodegradation of DDT in contami-nated soil. Preliminary lab-scale study. Part II. Substrates and pH control

“…1-4 as concentrations (μmol·(kg soil DM (dry mass)) -1 ) of DDT, DDD and DBP, in relation to the incubation time. Similarly as in the previous part [1] DDE level remained very low, thus minimizing production of DDD decisive for reduction of the DDX index (the sum of DDT and its primary metabolites DDD and DDE), required by soil quality standards [6]. DBP represents the final product of anaerobic DDT transformations [2].…”

“…The other substrates such as sucrose, potato starch, beet molasses and dried whey were purchased in local groceries. Concentrated phosphate buffer, methanogenic granular sludge and soils: contaminated NIE1 and clean NIE0 were the same or similarly prepared as previously [1].…”

“…Biodegradation tests. The general procedure of preparing biodegradation tests, their incubation and sampling have been presented elsewhere [1]. In experiments II and III, 20 mg of nitrogen per sample were added in the form of an ammonium chloride solution (discarded later as it was found not to be important to the results).…”

“…Gas chromatography (GC) analysis. Soil sampling, extraction and GC analyses were similar as in [1]. Measurements included p,p′ isomers of DDT, DDD, DDE (1,1-dichloro-2,2′-bis(4-chlorophenyl)-ethene) and DBP (4,4′-dichlorobenzophenone), which are given in the text without indication (p,p′) of the isomer type.…”

“…The paper presents another part of a study on anaerobic biodegradation of DDT (1,1,1-trichloro-2,2′-bis(4-chlorophenyl)ethane) in polluted soil. In the former part [1], the process enhancement by various doses of surfactant as well as influence of initial contamination level and DDT anaerobic degradation pathways have been examined. The issues addressed in the present paper are the role of additional organic substrate (electron donor), effect of its type and closely related issues of pH control during the treatment.…”