Environmental Engineering Reference
In-Depth Information
7.3.6.1 LTU objectives
The LTU study was designed in two phases, to evaluate several cultivation
and management strategies for the land farming of PAHs. Cultivation was
accomplished using a rear-tine rotary cultivator. In the initial phase, LTU 1
was cultivated at start-up to homogenize the soil and on day 71 to observe
the effect of tilling on microbial respiration. LTU 1 represented remediation
by natural attenuation. LTU 2, representing land farming with tilling, was
cultivated at 2-week intervals. The soil moisture in both LTUs was main-
tained at 50 to 80% of the soil field moisture capacity (FMC). Nitrogen
fertilizer was added to the LTUs twice. Liquid and solid forms of fertilizer
were used to establish both the optimal delivery method and the effect of
nutrient addition on microbial respiration. Nutrients were added prior to
tilling, in conjunction with moisture addition. Soil samples were taken every
2 weeks. The parameters included in bimonthly soil analysis were contam-
inant concentration, nutrient concentration (total Kjeldahl nitrogen (TKN)
and total phosphate (TP)), total organic carbon (TOC), pH, and moisture
content. Microbial biomass was evaluated initially and at various times
during the study. Microbial respiration, measured by soil gas analysis, was
monitored twice each week to follow changes in the oxygen and carbon
dioxide concentrations in the soil.
7.3.6.2 Trough study objectives
The experiment was designed to confirm, at the pilot scale, the improved
bioremediation of HMW PAHs using both biostimulation and bioaugmen-
tation as observed with flask trials. The efficiency and effectiveness of these
processes for land farming of PAHs would be compared. The nutrients,
bulking agent, and bacterial carrier were the same as those used in the flask
experiments. Bioaugmentation was performed with
P. aeruginosa
strain 64,
a biosurfactant producer known to survive in the POPILE soil.
7.3.7 Land treatment units: assembly
The pilot-scale LTUs were built to simulate actual land treatment systems
and consisted of a bottom impermeable liner, a sand bed leachate collection
system, and hard standing walls to withstand impact from cultivation. A
secondary containment cell was constructed, similar in concept to a landfill
liner (ASTM D-1973-91, modified), for added environmental security (Figure
7.9). Each completed LTU, as seen in Figure 7.10, was approximately 18 in.
deep, 4 ft wide, and 20 ft long (0.5 × 1 × 6 m). Complete construction details
are provided in Hansen et al. (1999).
7.3.8 Trough study: assembly
Three galvanized steel water troughs, 10 ft long × 3 ft wide × 2 ft deep (3 ×
1 × 0.6 m) were used as troughs to contain the contaminated soil and the
various amendments. The bottom of each trough was reinforced with 1/8-in.
