Liquid purification or separation – Flow – fluid pressure or material level – responsive
Reexamination Certificate
2001-09-26
2003-07-15
Prince, Fred (Department: 1724)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
C210S120000, C210S150000, C210S205000, C210S260000, C210S603000, C210S617000
Reexamination Certificate
active
06592751
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for treatment of wastewater. More particularly, the present invention relates to a device for the removal of biodegradable contaminants from wastewater using biological processes. The present invention also relates to a system for purifying highly contaminated water which contains a large amount of suspended solid impurities (TSS) and high concentrations of BOD (biochemical oxygen demand) and COD (chemical oxygen demand) as, for example, effluents from food processing plants and toilets. The device enables the efficient removal of biodegradable solid substances from wastewater by a combination of filtration and biochemical reaction. In other words, this invention relates to a bioreactor device that enables both biological degradation and the filtration of suspended solids.
BACKGROUND OF THE INVENTION
The treatment of wastewater for the removal of substances that cause BOD is best accomplished by biological treatment methods such as aerobic degradation and anaerobic degradation. There is a wide range of industrial operations that result in liquid effluents containing substantial amounts PBOD, which has to be removed to conform to national discharge regulations. In addition, several of these high-BOD industrial effluents, have substantial quantities of BOD present as suspended solid material.
In general, examples of BOD exerting suspended solids include, but are not limited to, partially dissolved and partially macromolecular materials, such as proteins, long-chain fatty acids, fats, vegetable oils, tallow, bacterial and yeast cell-walls, celluloses, hemicelluloses, and starch; the suspended solids being present in emulsified, suspended or colloidal state. Effluents of this nature are discharged for example, from slaughterhouses, dairies, rendering plants, oil mills, pharmaceutical and organochemical plants, pulp and paper factories.
The relevant organic compounds constituting biodegradable solid organic matter are generally classified as 1) Polysaccharides common among which are cellulose, hemicellulose, starch and pectin 2) Proteins and amino acids which are present as insoluble matter when coagulated by heat, acids or tannins and 3) Fats and long chain fatty acids. All these compounds can be degraded by anaerobic micro-organisms to form methane. The first step in the degradation process is called solubilization which results in the formation of soluble compounds and is carried out by enzyme action outside of the microbial cell. This is a slow process and requires sufficient microbial cells producing the enzymes and sufficient contacting time between enzyme and solids. In fact, the solubilization step is most often the rate limiting step in the sequence of anaerobic reactions that result in mineralisation of the polluting substances.
The development of high-rate anaerobic reactors, anaerobic treatment has become the economic option in the pretreatment of high BOD industrial effluents. However, high-rate reactors can be used only for the treatment of industrial effluent with BOD in primarily dissolved form. There are no high-rate reactor devices, in use, for the treatment of complex wastewater, i.e., wastewater containing un-dissolved BOD. A survey of prior art, has revealed no apparatus specifically designed to accomplish the primary object of this invention, i.e., the high-rate anaerobic treatment of wastewater containing suspended solids. Therefore, a survey of related art is given below, wherein, some ideas and concepts related to this invention may be found. This survey is merely in support of the practicality of the concepts used in this invention and does not in any way detract from the absolute novelty of the device.
PRIOR ART
Related Art in Anaerobic Treatment of Wastewater:
High-rate anaerobic reactors enable continuous treatment of industrial effluents at small hydraulic retention times. In other words, reactor sizes are relatively small and the BOD load per unit reactor volume per day is high. The primary principle that permits high BOD loading is the retention of a large population of viable microorganisms (biomass) within the reactor by decoupling the retention time of microorganisms from the hydraulic retention time. In simple language, the microbes stay within reactor longer than the liquid being treated.
A variety of high-rate anaerobic reactor systems are in commercial use. A good description of anaerobic processes and reactors is given by S. Stronach, T. Rudd and J. Lester, “Anaerobic Digestion Processes in Industrial Wastewater Treatment”, 1986, Springer Verlag, Berlin. The prominent designs can be classified into three families: 1) fixed-film reactors 2) sludge-bed reactors and 3) fluidized bed reactors. However, none of these prior art high-rate anaerobic reactor systems are suitable for the treatment of wastewaters where a substantial quantity of BOD is present as solid matter. This will be clear from closer examination of the operating principles and constructional features of these reactors.
The fixed-film reactors use a stationary inert packing media within the reactor on which microorganisms are retained as a biofilm. The function of the media is enhanced by the increasing the surface area. But the media should have sufficient open porous channels available for free flow with only minor hydraulic head loss and these channel should remain open even after copious growth of biofilm. Among various media types available, are dumped or random packing comprising rings like units and structured media constructed with corrugated plastic sheets jointed to form blocks with dividing straight channels. Both types of packing media are rapidly choked by the deposition of suspended solids present in wastewater. This is especially true in the case of fully submerged upflow type fixed film reactors. In a downflow configuration, the presence of solids in the wastewater will either lead to choking of media or if media has sufficient porosity and straight channels for free outflow of solids, there will be insufficient removal of BOD.
The sludge-bed reactors enable the retention by using the settling property of sludge which is denser than wastewater, if free of gas bubble inclusions. Specially designed “gas solids separators” are mounted on top of reactor to enable settling of sludge. While these reactors are affected by choking problems as is the case with fixed film reactor, they are still not suitable for the treatment wastewater containing solids. Solids in wastewater will rapidly attach or adsorb to the sludge, decreasing its specific gravity and impairing the settleablity of sludge. This lead to the phenomenon of sludge washout, a common and recurring cause of failure of several installations of such reactor. In general, sludge bed reactors are not recommended for wastewater with more than 30% of COD present as insoluble matter. The originator of UASB (upflow anaerobic sludge bed) technology, Professor Gatze Lettinga, from the Netherlands writes in his comprehensive review: “UASB process design for various types of waste-water”; Water Science and Technology, 24, 8, 87-107 (1991), “Regarding the reactor system to be chosen for treating a partially soluble complex wastewater it will be clear that process that apply a high superficial velocity, such as fluidized bed and expanded granular sludge bed (BOSS) reactors are unsuitable, unless they are combined with an adequate pre- or post-clarifier. According to our present experience, application of granular sludge UASB (or EGSB) reactors becomes doubtful at TSS-concentration in the influent exceeding 6 to 8 g/l because at such high TSS-concentration, the segregation between granular and flocculent sludge does not proceed sufficiently rapidly. For high strength wastewaters with high insoluble fraction, (i.e., exceeding 15%) generally conventional digesters are in favour over UASB and other high-rate systems.”
Fluidized bed reactor using small biofilm carrier particle in fluidized state is free of clogging, choking or sludge washout problems. But fluidized be
Council of Scientific and Industrial Research
Prince Fred
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