Environmental Engineering Reference
In-Depth Information
horizontal laterals, working face spray; and spray on yard waste composting over
intermediate cover (USEPA, 2007). Burlington County bioreactor in northwest New Jersey
had full scale leachate and liquid recirculation from 2002 to 2005 in a 4 hectare (10 acre) area
accepting about one million tonnes of MSW.
The New River Regional bioreactor was a “research” bioreactor in Union County, north
central Florida. It had about one million tonnes of waste in-place in an existing 5.07 hectare
(10-acre) area. Leachate was re-circulated into an existing interim capped landfill with an
exposed membrane cover. Volume of leachate re-circulated was about 24,600 m
3
(6.5 million
gallons) to date (USEPA, 2007). Salem County bioreactor in southwest New Jersey is another
anaerobic bioreactor with about 2 hectare (5-acre) area. Leachate re-circulated from storage
tank and force main to subsurface horizontal injection trenches has been performed since
2000. The rate of moisture addition is about 0.167 m
3
/tonne (44 gallons/tonne) waste
(USEPA, 2007).
Indicators of waste stabilization in these bioreactor landfills include settlement and gas
production. The airspace at CWC landfill had been monitored using airspace factor (AUF)
calculations. The cell was constructed in 1991 and recirculation began in 1998. Accordingly,
the pre- and post-recirculation AUF was 595 kg/m
3
(1004 lb/yd
3
) and 795 kg/m
3
(1,341
lb/yd
3
) respectively. In addition, CWC installed four settlement plates in 2000 and 2001 at the
waste level of two of the horizontal laterals. Data indicates that about 20% settlement has
occurred within 5 years (USEPA, 2007). Burlington County landfill bioreactor measures
quarterly settlement surveys with settlement plates and annual air photography surveys for
topographic comparisons. Substantial settlement over the last 4 years of operation was
observed increasing the effective density from 500 kg/ m
3
(840 lb/yd
3
) to over 720 kg/ m
3
(1,200 lb/yd
3
) (USEPA, 2007). The New River Regional Landfill measured the settlement
with GPS coordinates on the landfill surface with settlement of each nested vertical injection
well. The depth of settlement was the greatest at the injection well and declined with radial
distance from the well up to 15 m (50 ft) away and then leveled off. The data also showed a
distinct linear relationship between total settlement and the amount of moisture added
(USEPA 2007). The Salem County bioreactor showed a settlement rate of about 1.5 m (5 ft)
per year, which was greater than the rate observed before leachate re-circulation commenced
(USEPA 2007). Landfill gas was passively vented at Crow Wing County Landfill and
concentrations of methane had been as high as 60%.
At the Calgary biocell, the end of stage 1 will be determined using a combination of
settlement and gas generation readings. The gas production rate from October 2006 to
September 2008 is shown on Figure 12. The initial gas production rate was low, indicating
the microorganism acclimation stage. After leachate recirculation was initiated, the gas
production rate increased four-fold to 254 m
3
/h (150 cfm). Thereafter, the gas production rate
decreased gradually and reached a steady state flow rate of 170 m
3
/h (100 cfm) throughout
the winter months. The Calgary Biocell received 43,000 tonnes of waste over a period of
about one year. The methane generation potential, calculated from waste composition data, is
120 m
3
/tonne of solid waste. Hence, in October 2006 the theoretical gas generation rate at the
Biocell should be approximately 282 m
3
/h (166cfm) which is very close to the field measured
value of 254 m
3
/h (150cfm) reported in Figure 12.
