EFFECTS OF ALKALINITY AND HARDNESS
ON ANAEROBIC DIGESTION OF LANDFILL LEACHATE
John L. Carter, Process Engineer
Paul E. Schafer, Project Manager
Black & Veatch, Engineers-Architects
Kansas City, Missouri 64114
Russell T. Janeshek, Technical Manager
Gregory C. Woelfel, Regional Engineer
Waste Management, Inc.
Milwaukee, Wisconsin 53222
INTRODUCTION
The Omega Hills landfill, owned and operated by Waste Management, Inc. (WMI), is located 15
miles northwest of downtown Milwaukee, Wisconsin. The landfill accepts municipal, industrial, and
commercial wastes and has in the past accepted liquids and sludges. Waste Management has installed
a leachate collection system and is currently extracting leachate from the landfill. The leachate is
pumped into a sewer that leads to the Milwaukee Metropolitan Sewerage District (MMSD) South
Shore Treatment Plant. The Wisconsin Department of Natural Resources (WDNR) requested that
WMI provide a treatment system for the removal of 200,000 gpd of leachate. A paper presented at
the 39th Purdue Industrial Waste Conference describes the pilot plants used to evaluate anaerobic
digestion of the leachate and the first four months of pilot plant data [1].
The full-scale treatment system was designed to use two digesters operated in series to treat an
average flow of 200,000 gpd. This design also provided the capability to operate the digesters in
parallel. Leachate volumes from the landfill have declined significantly since design began; therefore,
only one digester was constructed. This digester is an upflow type anaerobic filter designed to treat
an average flow of 100,000 gpd and a maximum flow of 150,000 gpd. Startup is expected in the next
month. The original design was based on a loading of 340 pounds per day of BOD per 1,000 cubic
feet of media with the digesters operating in parallel. However, as a result of pilot studies, the filter
media volume was reduced which resulted in the organic loading being increased to 442 pounds per
day of BOD per 1,000 cubic feet of media. The early pilot plant data indicated that increased removal
efficiencies could also be expected at the higher loading.
The pilot plant study was begun using four units for evaluation: an anaerobic filter containing
media that allowed only vertical flow in the reactor (designated Digester One), an anaerobic filter
containing media that encouraged crossflow or horizontal flow in the reactor (designated Digester
Two in this paper), and two mixed contact type digesters. Each pilot plant had a total liquid volume
of 127 liters, and 3.54 cubic feet of plastic media was used in each of the anaerobic filters.
Performance of the contact digesters was inferior to that of the two anaerobic filters; hence, the
contact digesters were shut down in June 1984 and attention was concentrated on the anaerobic filters
(Figure 1). The first several months' data indicated that there was little difference in the operation
of the two anaerobic filters when fed at a given loading rate. Therefore, one reactor was loaded at
a much higher rate than the other to provide additional data and to reduce the testing period.
This paper describes the operation of the reactors after one year with an emphasis on the last
nine months of operation. High suspended solids and hardness concentrations are characteristic of
the leachate being studied and will be discussed as they pertain to the pilot plant's operation. The
biological production of high concentrations of alkalinity and its effects on the pilot plant's operation
will also be discussed.
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