IL31329A - A method of purifying sewage water with the aid of activated sludge - Google Patents

Description

SEWAGE A METHOD OP HJRIFYING/WATEB WITH THE AID OP ACTIVATED SLUDGE , . .

A METHOD OF PURIFYING WATER VITK THE AID OP ACTIVATED SLUDGE . .

This invention relates to a nethod of purifyin sewage /water with the aid of activated sludge in a purification plant having pools for aeration and sedimentation and/or flotation in which under the influence of the bacterial flora in the sludge the organic constituents of sewage water form sludge and flocks which are separated from the water, and the pools for aeration, sedimentation and/or . lotation are housed in premises separated from external air.

It is well known that the temperature of the sewage .water and ambient air greatly affects the functio at the biological purification of sewage water. Practical experiments have shown that the active bacterial flora has its maximum activity within a range of water temperature from between 7° and l4°C.

In purification plants located in countries where the temperature during sone parts of the year lies about or below 0°C it has been found that the desired biological degradation of sewage constituents is considerably impeded' when the water temperature by . Sails reason of the ccol ambient air -ea-nk-e and approaches a temperature range of from +2°C to + °C and practically altogether stops at temperatures about 0°C. For the elimination of this problem it has already been suggested to heat the sewage but for economical reasons such a solution is not feasible because of the very large quantities of sewage concerned.

The present invention is based upon the dis- the purification plant, irrespective of the seals-οη·, is approximately constant and as a rule lies in the range of from 7° to 14°0, i.e. the temperature is in se sufficient for maintaining a fully acceptable biological degradation process. However, owing to the effect of the air temperature, as already mentioned, the . tempera- falls ture of the sewage in v.'ir.ter ad-nlcs. in the previously kr.ov.'n purification plants to a temperature range of below ii°C and often to one or two degrees above 0°C and as mentioned above, this results in the biological process ceasing altogether. In practice, this implies that no appreciable biological purification of the sewage occurs in winter in the purification plants as presently used, where the sewage enters into intimate contact with the ambient air by way of mechanical aerat and in sedimentation pools having large water surfaces. What actually occurs in such purification plants may be attributed primarily to a purely mechanical sedi en-tationj and it follows from this that in winter sewage is allowed to escape in a practically non-purified state into the receiver. One solution of the above-mentioned problems is to locate the purification plant in premises insulated from external air, but in premises of so large capacities as those herein concerned and having so large open water surfaces it has been found extremely difficult to provide for a ventilation which is acceptable from hygienic, economical and functional aspects.

. The present invention has for its object to eliminate in an economically feasible way any delete- that are caused by temperature var at ons. o th s end, the method of the invention is characterised by the steps of arranging; neans for measuring the quantity and temperature of the influent in the purification the, plant, and providing neans for supplying to ee*^ pre- of the plant mises/an air volume adapted to the requirements of the biological process and to the ventilation of the pre- . mises, said air volume having a temperature at least equally high as and preferably some degrees higher than that of the influent, the air volume being controlled in relation to the quantity of influent and the air temperature being controlled in relation to said temperature of the influent.

The above method will be more fully described in the following with reference to the accompanying drawing which diagrammatically shows a purification plant adapted to operate in accordance with this invention.

The sewage enters the illustrated plant through the conduit 1 which is equipped with means 2 for separating solid matter and/or suitably a comminuting device 3· The comminuting device is of a construction that provides conuninution of solid natter in the sewage to a particle size of one or two ππ,, and this implies that such solid matter, if of organic origin, is influenced by and partakes in the biological degradation process. Mounted, in the supply conduit are means sensing the sewage temperature and a volumeter 5. It will be understood from the following how these apparatus function. From the inlet the sewage flows to per se known aeration pool . is then caused to enter a sedimentation and/or flotation pool 7 where it is kept for a given tine during which sludge and flocks *¾ϋ sink to the bottom or rise to the surface of the pool. The waste water fron said pool a receiving body of water may escape into ^hc-recel-wy, but it can also be treated in further steps for -renoval of nutritive salts and the like. The sludge separated in the sedimentation and/or flotation pool can either be transported to a sludge tank 8 or be returned to the aeration pool 6 there to activate the influent by reason of its bacteria content which has increased during the sludge separation. The sludge in the sludge tank 3 is preferably dewatered mechanically, whereupon it can be subjected to further treatment and preferably be exploited as a constituent part of soil improving compositions.

The novel features of the present invention reside in that the aeration pool as well as the sedimentation and/or flotation pools are disposed in premises 9 insulated and separated from external air, said premises having means 10 for controlled supply of. air. As mentioned in the introduction, it is not economically feasible to try to increase the tenperature of the sewage Instead, the tenperature of the supplied air is influenced in the method of the present invention. The tenperature of the air is determined by the tenperature of the influent with the aid of the earlier mentioned sensi means k so that the air temperature is kept higher than fall and does not a-inte below the water temperature- The supplied air volume is so adjusted to the quantity of process and the ventilation of the premises is supplied from the outside. Even if the external temperature is low and lies about or below 0°C the air need not thus be heated to more than a tenperature one or two degrees higher than that of the sewage. This implies in practice that the air temperature in the premises will be kept at or immediately below +10°C.

The application of the method described above, irrespective of the season, produces an active bacterial flora and a good flocculation of the impurities in the water. As a result, the efficiency of the biological process can be maintained at a high level and it follows that the biological purification of the sewage will be excellent. Keeping the air temperature above the water temperature will prevent moisture and condensation water from forming in the space above the pools.

While the invention has been described in a preferred embodiment in the foregoing with reference to the accompanying drawing those skilled in the art will readily understand that the invention can be modified within' the scope of the appended claims.

Claims (2)

1. A method of purifying sewage water with the aid of activated sludge in a purification plant having pools for aeration and sedimentation and/or flotation in which under the influence of the bacterial flora in the sludge the organic constituents of the sewage form a sludge and flocks which are separated from the water, and the pools for aeration, sedimentation and/or flotation are housed in premises separated from external air, comprising the steps of arranging means (4 and 5, respectively) for measuring the quantity and temperature of the influent in the purification plant, and providing means (10) for supplying to said premises an air volume adapted to the requirements of the biological process and to the ventilation of the premises, said air volume having a temperature at least equally high as and preferably some degrees higher than that of the influent, the quantity- c-f air^being controlled in relation / to the quantity of influent.

2. A method of purifying sewage water, substantially as hereinbefore described with reference to the accompanying drawing.