Liquid purification or separation – Processes – Treatment by living organism
Patent
1989-05-16
1991-01-01
Wyse, Tom
Liquid purification or separation
Processes
Treatment by living organism
210618, 210631, 210670, 210695, 210713, C02F 128, C02F 328
Patent
active
049815938
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a new process for sewage treatment. The process of the invention combines physico-chemical clarification using fine mineral or clay particles with anaerobic digestion of a concentrated sewage.
Sewage can be regarded as the water-borne waste products of man. Ever since man has gathered himself into large communities, the effective treatment and disposal of sewage has been a matter for concern. Initially, the problem was solved by discharge into tidal waters or an inland watercourse. However, with an increase in population density, this option became unworkable and some form of treatment became necessary.
The main aim of sewage treatment is to greatly reduce both the biological oxygen demand (BOD) of the sewage and the number of pathogenic organisms. Recently, the removal of inorganic nutrients (phosphorus and nitrogen) has also become important. Historically, both clarification in settling tanks and biological oxidation have been used. Biological oxidation can be achieved in lagoons, trickling filters or activated sludge plants, the particular process chosen depending on such factors as land availability, sewage strength and power costs. In an industrialized economy, the activated sludge process is usually selected because of smaller land requirements and the relative cheapness of power.
Up to date capital and operating costs for an activated sludge plant are difficult to obtain, but some idea of costs can be gained by taking historical costs and updating to the present. Analysis of cost information for the years 1968 to 1977 shows that, when indexed to 1986, a direct operating cost of approx. 10.cent./m.sup.3 is obtained, while the capital cost of a 38 ML/day plant is estimated to be A$16.times.10.sup.6. Amortization of capital cost over 25 years at 15% p.a. results in a contribution to total treatment cost of approx. 20.cent./m.sup.3. Total treatment cost of the sewage is thus of the order of 30.cent./m.sup.3.
With industrialization, sewage flows and, as a consequence, total costs have increased dramatically. While a large fraction of these costs can be attributed to the collection system (drains, sewers etc.), treatment costs are still a significant fraction of the total, especially when more stringent effluent standards are enforced. As a consequence, there is considerable incentive to reduce treatment costs, and recent efforts to apply anaerobic techniques to sewage treatment have had this aim.
The invention seeks to provide a process for the treatment of domestic sewage, which will significantly reduce total treatment costs. While conventional processes generally rely on aerobic biological oxidation, this process proposes to use a combination of efficient physico-chemical clarification with rapid anaerobic biological digestion. The reduction in treatment costs can be achieved by greatly reducing capital costs, while limiting operating costs to below those for the conventional process. As capital costs represent about two thirds of the total treatment cost, a significant cost reduction should result.
The first stage of the present process involves physico-chemical clarification of raw sewage or primary settled sewage. This part of the process derives from the so-called "Sirofloc" process for water clarification, various aspects of which are described in Australian Patents Nos. 512,553, 518,159 and 550,702, the full texts of which are hereby incorporated into the present specification. Basically, the Sirofloc process provides rapid and efficient removal of suspended impurities and coloured substances (turbidity and colour colloids) from water by treatment of the water with a finely divided particulate mineral or clay material (referred to as a "coagulant/adsorbent") the individual particles of which have a particle size of 10 microns or less and have a thin hydroxylated surface layer. A positive zeta potential on the surface of the coagulant/adsorbent particles is not considered necessary for the present process.
Operation of the Sirofloc process is often enhanced by the additi
REFERENCES:
patent: 3658697 (1972-04-01), Huether
patent: 3928191 (1975-12-01), Belasco
patent: 4053394 (1977-10-01), Fisk
patent: 4076615 (1978-02-01), Olesen et al.
patent: 4200524 (1980-04-01), Levin
patent: 4253966 (1981-03-01), Lebesque et al.
patent: 4315823 (1982-02-01), Witt et al.
patent: 4576718 (1986-03-01), Reischl et al.
patent: 4609469 (1986-09-01), Keoteklian
patent: 4626354 (1986-12-01), Hoffman et al.
patent: 4735725 (1988-04-01), Reischl et al.
Priestley Anthony J.
Woods Mark A.
Commonwealth Scientific and Industrial Research Organisation
Wyse Tom
LandOfFree
Sewage treatment does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sewage treatment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sewage treatment will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1994557