Liquid purification or separation – Processes – Treatment by living organism
Patent
1993-06-07
1995-04-18
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210626, 210150, C02F 308
Patent
active
054075785
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an improved method of treating waste water containing biodegradable matter and to improved plant for implementing the method.
DISCUSSION OF PRIOR ART
It is known to break down environmentally damaging matter in sewage or other waste water by means of bacteria (e.g. naturally-occurring microbes) and to encourage the growth of such bacteria and their digestion of the waste matter thus creating biomass layers of media of an RBC (Rotating Biological Contactor) which is supported partly in air and partly in the waste water. The RBC is slowly rotated to alternately immerse the biomass layers in the waste water and then to expose them to atmospheric oxygen.
Normally the waste water is led to the RBC from an upstream primary settlement tank and leaves the RBC to flow into a final settlement tank from which, now purified of at least the biodegradable material and suspended solids, it flows on to the environment.
The usual procedure is to allow plant throughput to be determined by the inflow of waste water and to dimension the treatment plant so that even on the expected maximum rate of input flow, an adequate residence time of the waste water in contact with the RBC will be obtained. Such an arrangement works well in most situations but in some extreme operating conditions (e.g. where biocidal chemicals and petrochemical-based cleaning agents may be periodically discharged in the waste water) a steady decline in operating efficiency of the plant has been noted which can only be resolved by putting the plant out of commission and cleaning out all solid and liquid material contained therein.
GB-A-2119357, EP-A-0161077 and U.S. Pat. No. 4729828 all disclose waste water treatment apparatus in which treatment is effected in at least two biological stages each containing a rotating biological contactor but there is no suggestion in any of these: documents that the upstream one of these two stages forms a part of a flow-balancing chamber for the apparatus.
By arranging for a biological contactor to form a part of the flow-balancing chamber, the plant is able to cope with waste water flows that at least occasionally contain toxic substances that do inhibit the capacity of the biomass to treat the biodegradable matter in the waste water. Because a minor part of the biomass available on the RBC is located in the flow-balancing chamber, this minor part can, if occasion requires, act sacrificially to absorb, or at least reduce, the toxicity and thereby prevent the flow of toxic substances into contact with the major part of the biomass on the RBC.
We have now found that by the simple expedient of providing flow balancing at the upstream end of the RBC (and optionally also by dividing the primary settlement tank into two) it is possible to provide plug flow conditions in the downstream part of the RBC and ensure that even if a significant proportion of biocides is present in the input flow, these can be effectively diluted in the primary settlement tank thereby ensuring improved biodegradation on the RBC, i.e. conditions approaching BOD removal kinetics which are essentially first order with respect to BOD at the resulting and applied mass BOD rates per unit area of RBC media per day.
The invention is equally applicable to a compact integrated sewage treatment plant designed to serve a single house (e.g. a "Biodisc",(RTM) plant having an RBC media bank housed in one tank with upstream primary and downstream settlement tanks) up to a large-scale treatment plant designed to serve a community of more than 1000 people where a septic (primary settlement) tank is likely to be provided separate from the RBC which in turn is separated from a humus or final settlement tank.
SUMMARY OF THE INVENTION
In its method aspect, the invention involves feeding a chamber containing a rotating biological contactor (RBC) with waste water from an inlet tank and discharging from the RBC-containing chamber into a humus tank, the RBC being divided into separated upstream and downstream sections, th
REFERENCES:
patent: 3428555 (1969-02-01), Kitagawa et al.
patent: 4468326 (1984-08-01), Kawert
patent: 4729828 (1988-03-01), Miller
patent: 5248422 (1993-09-01), Neu
Klargester Environmental Engineering Limited
Skillman Henry H.
Wyse Thomas
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