Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2000-07-27
2003-02-11
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S196000
Reexamination Certificate
active
06517723
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a wastewater treatment process, and more particularly toward an activated sludge treatment process using immersed membrane filters.
BACKGROUND ART
There is an ongoing need for reliable treatment of wastewater both for reuse of the water and in order to meet ever more demanding state and federal discharge quality standards. Of continued concern is the need to remove organic nutrients including phosphates and nitrogen which encourage the growth of water plants and algae which in turn result in degradation of the natural environment and assorted health concerns. The effective and reliable removal of pollutants from wastewaters, particularly carbonaceous materials and nutrients such as nitrogen and phosphorous, has become increasingly important in efforts to supplement and reuse existing municipal water resources. Typical wastewater treatment processes usually include multiple treatment areas that can be broken down into: (1) a preliminary treatment area; (2) a primary treatment area; and (3) a secondary treatment area. The preliminary treatment is concerned with removal of grit and damaging debris, such as cans, bath towels and the like from the untreated wastewater. This is usually a two stage process whereby the debris such as rags and cans are removed by screens and the grit and heavy inorganic solids settle out of the untreated water as is passes through a velocity controlled zone. Dissolved organics and organic nutrients are carried within the fluid stream as it passes from the preliminary treatment area.
A typical primary treatment area, which is an optional element of wastewater treatment, entails a physical process wherein a portion of the organics is removed by flotation and sedimentation. Usually 40-70% of the suspended solids are removed in the primary treatment area.
The secondary treatment area is usually a biological treatment process where bacteria are utilized under controlled conditions to remove nutrients or non-settling suspended solids and soluble organics from the wastewater. These materials would result in an unacceptable biological oxygen demand (“BOD”) if left untreated. A typical secondary treatment method is an activated sludge process in which the wastewater is aerated and agitated with an activated sludge then purged of a variety of microorganisms. Often this aerobic stage is combined with an anaerobic stage, i.e., a stage operated in the absence of induced oxygen, either soluble or derived from nitrites or nitrates (NO
x
), and an anoxic system, i.e., where oxygen is absent but nitrate is present. Phosphorus removal is accomplished in the anaerobic stage and de-nitrification is accomplished in the anoxic stage.
Daigger, U.S. Pat. No. 5,480,548, the disclosure of which is hereby incorporated by reference, discloses in considerable detail anaerobic-anoxic-aerobic secondary treatment processes. Daigger teaches a serial biological reactor consisting of an anaerobic zone, an anoxic zone and an aerobic zone. Daigger further teaches the desirability of an anoxic recycle (“ARCY”) of mixed liquor suspended solids (“MLSS”) from an anoxic zone to an upstream anaerobic zone. Daigger teaches that effluent from the bioreactor enters a conventional gravity separator from which treated effluent is decanted and return activated sludge is returned to an upstream anoxic zone. In addition to Daigger, Hawkins, U.S. Pat. No. 5,601,719, Marsman, U.S. Pat. No. 5,342,522, Strohmeier, U.S. Pat. No. 5,798,044, Hong, U.S. Pat. No. 5,650,069, Timpany, U.S. Pat. No. 5,354,471, Wittmann, U.S. Pat. No. 4,961,854, Nicol, U.S. Pat. No. 4,787,978 and Yang, U.S. Pat. No. 5,942,108, each disclose multi-zoned bioreactors with some recycling of flow between the various zones to maintain concentrations of useful microorganisms and to improve biological nutrient removal. In each case, however, these patents teach conventional gravity separation by a clarifier or the like, as discussed above with regard to Daigger. One problem with gravity based separation systems is that the solids concentration must be limited in order to effect acceptable levels of gravity clarification. In addition, these systems do not provide a physical barrier to dangerous pathogens such as Giardia and Cryptosporidium. Furthermore, these processes are ineffective for the removal of a wide variety of dissolved organics.
Tanaka, U.S. Pat. No. 6,007,712, teaches a multi-zoned bioreactor wherein the separation of suspended solids occurs at a membrane module. Tanaka provides that non-permeating water which does not pass through the membrane is returned and circulated to a nitrification or aerobic tank. Tanaka also teaches that the membrane of the membrane filter is preferably hydrophilic to make it more difficult for suspended solids to attach and foul the membrane. Tanaka further provides that periodic back washing “by means of an air and a permeated liquid when the suspended solids component is attached” can be performed to purge the solids from the membrane. Tanaka teaches that recycle to the aerobic zone is required because only one seventh ({fraction (1/7)}) of the water present at the membrane can be filtered, thus requiring that the remaining water be returned upstream. Tanaka is silent whether it would be useful or desirable to recycle water if the membrane module were immersed within a hydrafication (or aerobic treatment) tank. In any event, Tanaka does not teach continuous aeration of the membrane module that would provide an oxygen charged MLSS for recycle to an aerobic zone. Tanaka also fails to provide for suitable removal of shock loads of organisms, such as may result from a toxic spill.
Anselme, U.S. Pat. No. 5,364,534, discloses a process for purifying and filtering water including introducing a pulverulent reagent, such as activated carbon, into a water stream downstream of a gravity separation and upstream of a membrane separation. The pulverulent reagent is recycled from the purge of the membrane separation to upstream of the gravity separation. Anselme does not provide for removal of biological nutrients and BOD and is thus of limited utility in treating municipal wastewater and many other sources of biological nutrient and dissolved organics containing waste water.
The present invention is directed toward overcoming one or more of the problems discussed above.
SUMMARY OF THE INVENTION
A first aspect of the present invention is an apparatus using activated sludge for the removal of biological nutrients from a wastewater. The apparatus includes a bioreactor for containing a mixture of wastewater under treatment and activated sludge. The bioreactor is divided into a plurality of serially connected treatment zones and includes a wastewater inlet, a downstream aerobic zone and an upstream aerobic zone between the wastewater inlet and the downstream aerobic zone. A membrane filter is provided in the downstream aerobic zone so that it functions as an immersed membrane filter with a bioreactor containing an operative volume of wastewater and activated sludge. The immersed membrane filter filters treated water flowing from the bioreactor through a first outlet. An aerator is operatively associated with the membrane filter for purging solids from the membrane filter with air or a gas including a select concentration of oxygen. A second outlet in the downstream aerobic zone is connected to an inlet in the upstream aerobic zone for recycling activated sludge charged with oxygen from the downstream aerobic zone to the upstream aerobic zone.
A second aspect of the invention includes a treatment tank having an inlet and a downstream outlet with the inlet coupled to the first outlet of the bioreactor for receiving treated water. A powdered activated carbon (“PAC”) supply provides PAC to the treatment tank near the treatment tank inlet. A membrane filter is operatively associated with the downstream outlet and is situated so that it functions as an immersed membrane filter with the treatment tank containing an operative volume of treated water. A coagulant supply may al
Broderick Thomas A.
Daigger Glen T.
Fleischer Edwin J.
Murthy Sudhir N.
Wollmann Albert M.
Barry Chester T.
CH2M Hill Inc.
Swanson & Bratschun LLC
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