Biotreatment of Sludge Impacted by Organic Wood Preservatives
Adventus conducted laboratory and field-scale pilot studies to demonstrate the effectiveness of aerobic DARAMEND® bioremediation technology to treat soil (lightly impacted) and sludge (heavily impacted) by organic wood preservatives (creosote [polycyclic aromatic hydrocarbons; PAHs] and pentachlorophenol [PCP]). Laboratory studies conducted to support field-scale designs included a control (i.e., sludge only) and a number of aerobic treatments, each consisting of one or a combination of the following parameters; (i) soil moisture content adjustment, (ii) addition of DARAMEND® bioremediation products, and (iii) addition of inorganic nutrients (i.e., phosphorus and nitrogen). Soil treatment consisted of biweekly monitoring of pH and soil moisture content plus manual mixing of the soil/sludge to promote oxic conditions.
Treat soil lightly impacted and sludge heavily impacted by organic wood preservatives (PAHs and PCPs).
Substantial removal of CPs was achieved after 150 days of DARAMEND® treatment (Table 1). The highest removal efficiency (>99%) occurred with the 10% sludge/90% soil mixture. Here, total CP concentrations were reduced from 392 mg/kg to 1.97 mg/kg (n=2). Effective removal of CPs was also achieved in treatments with higher sludge content. For example, a 91% reduction (from 1,126 mg/kg to 101 mg/kg total CPs) was achieved with a 40% sludge content. Substantial removal of PAHs was also achieved after 150 days of DARAMEND® treatment (Table 2). The highest removal efficiency (>95%) also occurred with the 10% sludge/90% soil mixture, which supported a reduction in total PAHs from an initial concentration of 219 mg/kg to 10.14 mg/kg (n=2) following 150 days of treatment. Leachability studies have shown these patterns of removal to support the position of using alternative end-points because the residual PAH constituents are not bioavailable (i.e., biostabilization).
The biological processes required at least 60 days of acclimation (lag time) before biodegradation of PCP commenced (Figure 1). The treatment regimes with a higher percentage of sludge required a slightly longer lead time. Ultimately, the treatment regimes with the lower proportion of the heavily impacted sludge (10 or 20%) mineralized 35 to 50% of the added radiotracer; mixtures containing 40% sludge mineralized approximately 30% of the 14C-PCP within the first 150 days of treatment. Removal of both CPs and PAHs continued with extended incubation time, which suggests that treatment beyond 150 days would result in even lower residual concentrations of monitored organic constituents.
Depending on material end use, the site-specific remedial objectives range from 3 to 20 mg/kg for PCP and from 10 to 100 mg/kg for total PAHs. These data proved that the various soil/sludge mixtures could be effectively bioremediated using the aerobic DARAMEND® technology. Field-scale pilot studie sare scheduled to begin in early 2004 using approximately 25 yd3 of three soil/sludge mixtures (9:1, 4:6 and 2:8 ratios).
The estimated cost of treatment for the 4:6 materials ratio is approximately $100/yd3, assuming a 12-month treatment time to reach the industrial standards and 15-months of treatment time to reach the lower residential standards.