Professor, School of Biology, Chemistry and Ecology, State University of New York College of Environmental Science and Forestry, Syracuse, New York.
From "Research Needs -- Sludges and Invertebrates: Should Invertebrates be Considered in the Final Step of the Wastewater Treatment Process?" -- Soil Absorption of Wastewater, Colorado State University, June 1-3, 1983.
THE potential use of M. domestica at wastewater treatment plants has not been tested to date. However, several thousands of gallons of flesh fly larvae are produced weekly on discarded animal scraps from local abattoirs (1). The flies scale the wall of a pit after they have achieved a critical stage of larval development. After reaching the outer side of the wall, they crawl into a bedding of sawdust that lies within a groove around the perimeter of the pit. Before pupation can occur, however, the larvae are collected by vacuum, separated from the sawdust by being sieved with a screen, stored at 5 deg C, and sold as fishing bait to European markets.
The housefly (Musca domestica L.) has been able to pass its entire life cycle (2) upon an activated sludge that had been obtained from a local brewery and shown to be lethal within several hours of contact with E. foetida [Eisenia foetida earthworms] (3). This sludge exhibited a conductivity in excess of 20 S cm-1, a value known to be detrimental to E. foetida (4). M. domestica also went through its life cycle on an anaerobic digest (2), a sludge which kills E. foetida within hours to a day or two (4).
At 20 to 25 deg C specimens of M. domestica hatch from eggs 42 times faster (0.5 d) than E. foetida hatches from cocoons (three weeks; 18). M. domestica matures sexually about four weeks after hatching (5), compared to about six weeks for E. foetida (6). I calculated that in a 21-week period at 20 to 25 deg C, assuming appropriate culture conditions and zero mortality, approximately 2.7x10 8 [2,700,000,000] flies in various developmental stages can be produced from a single female (7). Independently of differences in biomass per organism, this figure significantly exceeds 316, which is the number of hatchlings of E. foetida that can be produced in the same period starting with a single sexually-mature earthworm (8). An even larger number of houseflies -- 1.4x10 9 [14,000,000,000] -- can be produced in the same period if one assumes a stable age distribution has been achieved.
A managerial advantage to using flies is their self-harvesting capacity. Larvae migrate toward slightly drier conditions than are found in the moist sludge (probably 8% solids) which nurtured them. Suitable traps can be established to collect them, as indicated earlier (1). Alternatively, pupation may be allowed, after which the emerging adults can be attracted to incandescent lures and trapped in vacuo. The high nitrogen content of flies, the presence of much of their nitrogen as chitin, a commodity (9), the ease of harvesting flies, the possibility that flies are strictly microbivorous and do not require cellulose in their diet, the possibility that a proportion of their biomass is produced from human pathogens, and the likelihood that humification may proceed more rapidly in the wake of their activities rationalizes the concept that they may indeed be suitable tools in the management of sludge. Is it worth developing the necessary science to make this technology a real possibility? Alternatively, in view of an apparent high degree of success in resolving the three major problems of sludge management -- human pathogenicity, heavy metal phytotoxicity, and economic costs of sludge disposal -- should the bulk of research effort in sludge management be directed toward methods that can be used for converting sludges into building materials, such as bricks (10)?
Sludges produced freshly either anaerobically or through the activated aerobic process are microbial communities with varying amounts of cellulose and other undecomposed organic material. The wastewater treatment process can possibly be terminated by assimilating the microbes into soil invertebrates in situ and allowing humification to proceed. As an alternative procedure, houseflies, rich in chitin as a commodity, and nearly self-harvesting, might be deployable.
On-site visit to Bedford Brand Supplies, Irthlingborough, England (1980).
Brezner, J., Unpublished experiments, SUNY College Envt. Sci. and Forestry, Syracuse, New York (1981).
Kaplan, D. L., E. F. Neuhauser, M. R. Malecki and R. Hartenstein, Soil. Biol. Biochem., 12, 347, (1980).
West, L. S., The Housefly, Comstock, Ithaca, New York (1951).
Neuhauser, E. F., R. Hartenstein and D. L. Kaplan, Oikos, 35 (1980).
Pielou, E. C., Mathematical Ecology, John Wiley and Sons, New York (1977); collaborative effort was provided by Dr. N. H. Ringler.
Hartenstein, R., E. F. Neuhauser and D. L. Kaplan, Oecologia. 43 325 (1980).
Austin, P. R., C. J. Brine, J. E. Castle and J. P. Zikakis, Science 212, 749 (1981).
Alleman, J. E., N. A. Berman and M. F. Prouty, Solidification, encapsulation and stabilization of industrial wastes, 37th Annual Purdue Industrial Waste Conference (1982).