Costs for disposal of sludges from a municipal wastewater treatment plant normally represent at least 25 YO of the total plant operating cost. The most popular ultimate disposal options and rough estimates of the extent of use are as follows:
Landfill Land application Incineration Ocean dumping Total
Percent of sludge 25-30 25-30 25-30 15
Amount (dry solids, tons/ day) >4000 >4000 >4000 2500 >14 500
Sludge handling options considered are shown schematically in Figure 1. Option 1 includes two possible sludge dewatering processes prior to incineration: vacuum filtration to produce a 20% solids cake (Option la), or filter press dewatering to produce a 40% solids cake (Option 1b). Option 2 substitutes thermal conditioning of the sludge for the chemical conditioningof Option la. Option 3 involves essentially complete oxidation of the sludge while in the liquid phase. Option 4 includes two possibilities prior to land application or landfill disposal: aerobic digestion (Option 4a) or anaerobic digestion (Option 4b). Option 5 produces a dry ( l o mgd). The last thermal processing option (Option 5) is particularly sensitive to the market price of the final fertilizer product. The net cost to the municipality drops by $10lton for every $10/ton increase in the price of the product. However, a price of $40/ton of product would be requiredto yield a total cost to the municipality comparable to that for the two low-cost incineratwoptions (Option 1b and 2). The concentrationof the sludge solids going to the dryer would have to be increased from the currently assumed 25% to 40% to make this option competitive with incineration at a fertilizer product sale price of $30. Thus, for the 10-mgd plant size, incineration of municipal sludge that has been treated to produce a 40% sludge solids
TABLE 3
Unit costs piam size (ADWF) 10 mgd
100 mgd
. 500mgd
Electric power Cost (QlkWh) 2 1.5 1.5 Fuel 52/106Btu Operating and maintenancellabn 56lh Chemlcals Lime %25/ton __. . .... Ferric chloride (FeCb) 5134lton Polymers $10001ton Supplies All maintenance and operating supply costs were adjusted to a mid-I975 Whole Price Index for Industrial Commodities of 170. Hauling costs 50.1-0.2ltonlmile: 15-30 miles 53Iton of slurry or dry ash Landfill disposal 5lIton of slurry or dry ash
Volume 1 1 , Number 10, October 1977 971
Martek, the specialist in environmental data acquisition, now offers the Series DAS, an economical, flexible data acquisition system to meet a wide range of applications and provide logging and retrieval of data from environmental instrumentation. The heart of the Series DAS is the rugged, expandable DLS Data Logger which can record up to 99 analog or digital signals plus day and time of day, and can be operated on AC or DC power.The companion Model
Martek makes the difference in data acquisition. DRS Data Reader features a digital LED display which permits visual reading of the tape while the information is simultaneously available at the output connectors for external data processors.The Model EDP Environmental Data Printer records - continuously or intermittently- up to 15 data signals and time of day on a magnetic tape cassette and/or digital paper printer. The Series DAS, with its variable recording program, is ideal for data monitoring over long time periods in either portable or fixed station applications. Like the Martek microprocessor-based data acquisition system -the Model DMP- the Series DAS provides a permanent record of such environmental parameters as water quality, air quality, and meteorological data.
content ( 2 6 0 % volatiles) is competitive with a wide variety of other sludge handling techniques. This assessment is based on a comparison of capital and O&M costs, as well as on an analysis of fuel and electrical power consumption. As the plant size increases, incineration may provide lower capital and operating costs. Moreover, the thermal processing solution eliminates major management and institutional questions involving the final disposition of large quantities of sludge that must ultimately be disposed of on, or in the land.
Jerry L. Jones is manager of the Environmental Control Group at SRI International. He has extensive experience in wastewater treatment technology and related fields, and has worked in a number of states in the U S . , and countries overseas. Jones is a registered professional engineer in California and Illinois. David C. Bomberger, Jr., is a chemical engineer in the Environmental Control Group at SRI International.He specializes in industrial wastewater treatment process development and design; mathematical simulation; and optimization.
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For the full story on the full line of Martek data acquisition systems, write to: 0
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MARTEK INSTRUMENTS, INC.
F. Michael Lewis is a consultant in waste combustion systems, related energy recovery, and similar fields. He is a registered professional engineer in New York and Ohio.
Joel Jacknow is an independent consultant in environment and energy, with 10 years of experience in these fields. Previously, he supported the regulatory development process at €PA headquarters.
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