Ask Dan, the Wastewater Wizard

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Someone recently asked, “What are the wastewater treatment options for landfill leachate?”

According to statistics from the U.S. Environmental Protection Agency, the number of landfills in the United States is 1,654. And according to CNBC, active landfills handle more than 250-million tons of trash created in the United States each year. Statistics suggest that landfills can be breeding grounds for disease.

Perhaps the largest landfill in the United States is located in the state of Washington. It covers a 2,545 acre area, has a 120-million-ton capacity and a 40-year expected trash-receiving life.

The facility receives nonhazardous solid wastes only, predominantly municipal solid waste (MSW), from throughout the Pacific Northwest, including Oregon, Washington, British Columbia and Alaska. 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.

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.

Defining and sourcing

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. Nutrient imbalance can cause difficulties in maintaining an effective biological treatment stage. The treated liquor is rarely such that it can be released to the environment and, that being the case, it is typically transferred by tankers or piped to a local sewage treatment facility.

Treatment options

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 to analyze at least the following:

Constituents including but not limited to pH, nutrients, BOD, TOC, COD, suspended solids and metals should be examined. Likely, the next consideration is the range or maximum value limits of the treated wastewater in order to satisfy the regulatory-discharge permit. The permit will likely include flow and pH range along with the concentration & mass poundage of the other compounds.

With the untreated values and also the discharge-permit limits in hand, the information is at hand to determine the treatment requirements.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 & the Discharge Permit Limit for discharge 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 remove Zinc.

Obviously things like tank size, instrumentation, pumps, pipes, valves, chemicals, procedures and documentation need to be considered.

I encourage you to submit process questions treating your wastewater including but not limited to Landfill Leachate.

In my next article I will answer the questions you submit to me!

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About Dan Theobald:

Known in the industry as “Wastewater Dan,” Daniel L. Theobald, proprietor of Environmental Services, is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on industry experience operating many variants of wastewater treatment processing units and is eager to share with others his knowledge about water conservation. (www.ConserveOnWater.com).

Theobald serves as an active consultant for industries looking to achieve and maintain improved wastewater treatment at reduced cost. He is a Lifetime Member of the Who’s Who Registry of Professionals and holds numerous certifications from wastewater management regulatory boards and professional organizations. Theobald contributed one chapter to the Water Environment Federation’s (www.wef.org) Manual of Practice # 29 (MOP-29), a technical manual resource guide for biological nutrient removal, scheduled for publication in 2013. He also authors an industry-related blog (http://TheWastewaterWizardBlog.com/).

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