Liquid purification or separation – Processes – Treatment by living organism
Patent
1992-01-24
1994-12-27
Upton, Christopher
Liquid purification or separation
Processes
Treatment by living organism
210624, 210625, 210903, 210906, C02F 330
Patent
active
053762754
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to wastewater treatment. The invention is particularly useful in the treatment of raw sewage.
BACKGROUND ART
Modified activated sludge processes have been used for the removal of nitrogen (N) and phosphorous (P), but in many cases the expected performance has not been obtained. Frequently, both N and P levels in treated sewage are found to be many times those encountered in similarly designed plants operating on different sources of sewage.
One well known design of nutrient removal process is the Bardenpho process, described in South African patent application 72/5371 to the South African Inventions Development Corporation (equivalent to U.S. Pat. No. 3,964,998).
For example, this process is known to operate well in one suburb of Johannesburg, but to perform very poorly in another. It has been postulated that sewage deficient in acetic acid, a well known fermentation product, is not suitable as influent to activated sludge plants designed for the removal of P. Therefore attempts have been made to improve the performance of plants by subjecting the influent raw sewage or the settleable portion thereof to fermentation with the objective of generating acetic acid (Barnard 1984).
This procedure has been found to be of assistance. However, the generation of acetic acid is limited by the well known fact that relatively slow growing bacteria are capable of degrading acetic acid to methane. Thus the system has previously been optimised to minimise loss of acetic acid by limiting the mean cell retention time in the pre-fermenter. Mean cell retention time (MCRT) is defined as the average time spent within the system by a cell. In the sewage treatment industry MCRT is usually called "sludge age".
Prior workers have recommended that mean cell retention times be restricted to 5 days or less in order to maximise the production of acetic acid (Nicholls et al. 1987, T'Seyen et al. 1985).
DISCLOSURE OF THE INVENTION
Although the prior recommendations are broadly correct with respect to the generation of acetic acid, we have found that the efficiency of P and/or N removal increases with "soluble" carbonaceous substrate (soluble TOC) in the influent to the activated sludge plant. We have found that longer mean cell retention times (for example, in the range of 10-60 days) are more advantageous with respect to the N and P removal performance of an activated sludge plant such as the Bardenpho plant using sewage pretreated as described.
It is an object of the present invention to provide a process for the control of N and/or P levels in effluent from an activated sludge plant.
Accordingly, in a first aspect, the present invention provides a method of controlling the phosphorous and/or nitrogen level in effluent from an activated sludge treatment plant comprising providing a source of wastewater such as raw sewage, carrying out fermentation of the sludge component of said wastewater for a period exceeding that required for optimal acetic acid production and supplying the resultant product to said activated sludge treatment plant.
Where reference is made herein to a fermentation period required for optimal acetic acid production, we mean that MCRT previously recommended for optimal production, that is, 5 days or less.
A portion of the settled material resulting from the fermentation step of the invention may, if desired, be combined with other settled sewage before being introduced into the activated sludge plant.
Preferably the MCRT is substantially greater than that previously recommended for optimum acetic acid production. More preferably the mean cell retention time is in the range 10-60 days. A cell retention time of about 30 days is particularly preferred.
The activated sludge plant may be a 5 stage Bardenpho plant however, other activated sludge plants may be used. We have found that the level of phosphorous and nitrate in the effluent from a Bardenpho plant fed with raw sewage treated in a pre-fermentation tank fell from 5.3 and 1.5 mg/l respectively at 7 days mean cell retent
REFERENCES:
patent: 1439406 (1922-12-01), Elrod
patent: 2875151 (1959-02-01), Davidson
patent: 3166501 (1965-01-01), Spohr
patent: 3202285 (1965-08-01), Williams
patent: 3681236 (1972-08-01), Bergles et al.
patent: 3964998 (1976-06-01), Barnard
patent: 4874519 (1989-10-01), Williamson
patent: 4885093 (1989-12-01), Schoenberger
patent: 4919815 (1990-04-01), Copa et al.
patent: 5071559 (1991-12-01), Bleeker
R. C. Bayly et al, "The Effect of Primary Fermentation on Biological Nutrient Removal", Australian Water and Wastewater Association, 13th Federal Convention, Canberra, Mar. 6-10, 1989; pp. 162-166.
H. A. Nicholls et al, "Improvement to the Stability of the Biological Phosphate Removal Process at the Johannesburg Northernm Works", Biological Phosphate Removal From Wastewaters, ed., R. Ramadori, pp. 261-272 (1987).
T'seyen et al, "Proceedings of International Conference on Management Strategies for Phosphorus in the Environment", Lisbon, Jul. 1-4, 1987, pp. 216-217 and 220.
Korrespondenz Abwasser, vol. 36, No. 3, Mar. 1989, pp. 337-348.
GWF: Das Gas- und Wasserfach, vol. 130, No. 2, Feb. 1989, pp. 49-56.
Commonwealth Scientific and Industrial Research Organisation
Upton Christopher
LandOfFree
Wastewater 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 Wastewater treatment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wastewater treatment will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-916628