What are the treatment options for landfill leachate?
New contributor to Water/Waste Processing aims to answer readers’ most pressing questions
It’s said the United States has 1,654 landfills, handling more than 250-million tons of trash each year.
One Washington landfill covers a 2,545-acre area, has a 120-million-ton capacity and a 40-year expected trash-receiving life.
The facility, the Republic Services-Roosevelt Regional Landfill in Roosevelt, Wash., receives nonhazardous solid wastes only, predominantly municipal solid waste (MSW), from throughout the Pacific Northwest. Solid wastes are delivered by waste-collection and transfer vehicles.
However, approximately 95% of the waste the facility receives comes in by rail haul via the Burlington Northern Santa Fe Railroad. Waste is received primarily in inter-modal containers, which are unloaded from flatbed rail cars and placed on trucks for a 4.5-mile short-haul to the landfill along the private haul road.
Defining and sourcing
The landfill accepts residential, commercial and industrial waste streams, including MSW, construction and demolition debris (CDD), wood wastes and petroleum-contaminated soils, as well as non-dangerous dredged sediments, treated medical wastes and other special wastes. Municipal incinerator ash is also accepted at the double-lined ash mono-fill at the facility. There is no on-site treatment.
Landfill leachate is the name given to the liquid materials that drain from land or stockpiled materials and that may contain significantly elevated concentrations of undesirable material derived from that which it has passed through.
Leachate from a landfill varies widely in composition, depending on the landfill’s age and waste type and usually involves both dissolved and suspended materials. Leachate is generated principally by precipitation percolating through waste in a landfill deposit. The percolating water is contaminated by contact with decomposing solid waste and, if it then flows out of the waste material, it is termed leachate.
As water percolates through the waste, it promotes and assists the work of bacteria and fungi. Decomposition releases by-products and rapidly uses up any available oxygen, creating an “anoxic” environment. In actively decomposing waste, temperatures rise and the pH falls rapidly. Therefore many metal ions that are relatively insoluble at neutral pH can dissolve in the developing leachate. The decomposition process itself releases further water, which adds to the leachate volume.
On-site treatment is the most common way of handling collected leachate. When treating leachate on site, it is pumped from the sump into treatment tanks. The leachate may then be mixed with chemical reagents to modify the pH, coagulate and settle solids and reduce hazardous-matter concentration.
A modified form of biological treatment can further substantially reduce the dissolved organic content. The treated liquor is typically transferred by tankers or piped to a local sewage treatment facility.
First learn the chemical makeup of the liquid leachate wastewater to determine its process requirements. Conduct multiple events to collect liquid untreated wastewater, and use a regulatory approved environmental laboratory.
Analyze constituents including but not limited to pH, nutrients, BOD, TOC, COD, suspended solids and metals. Likely, the next consideration is the range or maximum value limits of the treated wastewater in order to satisfy the regulatory-discharge permit.
Some possible conditions for consideration may include the following:
Flow: the allocation may be limited to 50,000 gallons per day (GPD).
pH: the untreated value may be less than 6.0 pH units & the pH range for discharge may be between 6.0 and 9.0 pH units.
COD (Chemical Oxygen Demand): the untreated value may be greater than 50,000 Milligrams per Liter (Mg/L), however the discharge permit limit may not be specified.
BOD (Biochemical Oxygen Demand): the untreated value may be greater than 25,000 Mg/L and the discharge permit limit for may be 225 Mg/L.
Ammonia: the untreated value may be greater than 750 Mg/L and the discharge permit limit for may be 50 Mg/L.
TSS (Total Suspended Solids): the untreated value may be greater than 1,400 Mg/L and the discharge permit limit may be 250 Mg/L.
Oil & Grease: the untreated value may be greater than 400 Mg/L and the discharge permit limit may be 100 Mg/L.
Zinc: the untreated value may be greater than 15 Mg/L and the discharge permit limit may be .500 Mg/L.
In treating this wastewater, it will be required to treat 25,000 Mg/L down to 225 Mg/L. Consider oxidation or a conventional secondary-treatment process. However, some treatment processes may not be as obvious, for example the treatment of TSS and O&G may occur while dedicating a hydroxide precipitation process to zinc removal.
Obviously things like tank size, instrumentation, pumps, pipes, valves, chemicals, procedures and documentation need to be considered.