Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-12-03
2001-09-18
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S626000, C210S631000, C210S195200, C210S195300, C210S257200
Reexamination Certificate
active
06290852
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention resides in a process for the purification and/or treatment of communal and/or industrial waste waters particularly for use in marine facilities and an arrangement for performing such a process.
Besides community wastewater processing plants, which are installed to treat the wastewaters from relatively large areas, there are communal and/or industrial wastewater flows, which must be processed or purified locally before they can be discharged into the environment. There are generally three types of decentralized plants with which wastewaters can be purified or, respectively, treated. These are plants found, for example, in communities which are not connected to central communal wastewater treatment and purification plants (case 1). The industrial wastewater treatment for problematic compounds, which, because of unfavorable ratios, have concentrations of CSB to BSB
5
(case 2), which cannot be treated in conventional purification or, respectively, treatment plants.
The wastewater treatment in marine facilities such as ships (case 3) poses a particular problem.
Especially in cases 1 and 3 wastewaters of a highly variable composition must be treated. Also, the volume flows vary widely. In case 3, additionally the conditions existing in marine facilities such as ships must be taken into consideration.
Particularly for use in marine installations, for example on board of ships, very rigid rules have been established by international organizations such as the IMO (International Maritime Organization) governing the release of contaminants from marine facilities into the sea. The limits set by these organizations are in some cases substantially lower than the limit values for the discharge of treated wastewaters from land-based stationary treatment and purification plants. Since the seas and, increasingly, sensitive water bodies such as the Arctic and the Antarctic are visited by research vessels and fishing boats and now also by passenger ships (cruise ships) very rigid rules have been established. In the past, the wastewater generated in marine installations has been collected in tanks, at least while a ship was in a harbor or in national waters and was then discharged into the sea in international waters, often without having been reliably purified. In fact, often the wastewater has been discharged without any purification or treatment so that all the waste and contaminants were released into the sea.
This is unacceptable for the reasons given above and will not be permissible in the future. On the other hand, on-board treatment of wastewaters on marine installations requires highly compact equipment because of the limited space available. In addition, the equipment must not be affected by the rolling motion of ships, that is, the treatment apparatus must remain fully operative even if the ship is not stable. Furthermore, the wastewater flows in ships are generally not separated, that is, in effect they represent a mixture of communal and industrial waste waters. Particularly with the introduction of technical solutions (grease, cleaners, tensides, disinfectants, etc.), the ratio of CSB/BSB
5
increases above that common in communal wastewaters. Also, changes may be very sudden. Because of the low content of microorganisms present in conventional reaction systems with maximal bio-mass concentrations of 5 g/l, such sudden changes cannot be accommodated. As a result, the biological decomposition of the waste material is much decreased.
It is therefore the object of the present invention to provide a process and apparatus for the purification of wastewater streams, which may be subjected to highly variable hydraulic loads as they are present in marine installations such as ships. The treatment should be quasi-continuous and in a quasi-closed system and should not require any maintenance or attendance by personnel. The process and equipment should also be simple and relatively inexpensive.
SUMMARY OF THE INVENTION
In accordance with the method of the invention, the wastewater to be purified, or respectively, to be treated is supplied to a biological reaction apparatus, which includes suspended therein a bio-mass of high concentration. After treatment in the reaction system, the treated wastewater is supplied to a membrane separation apparatus, in which it is separated into a permeate and a retentate and wherein the permeate is either discharged as useable or pure water or is at least partially returned to the reaction apparatus.
The advantage of the method according to the invention resides essentially in the fact that, with the high bio-mass concentration, the wastewater to be purified reaches already at the exit of the reaction system concentrations, which are not achieved with conventional systems. It is furthermore an important advantage that clean water is separated from the waste water in the membrane separating apparatus in a one-step process, whereas, in conventional systems, viruses and bacteria cannot be eliminated in a single process step. In addition, the process is performed quasi-continuously in a closed circuit.
In an advantageous embodiment of the method, the retentate is at least partially returned to the reaction system for example when sufficient wastewater for purification and treatment is provided.
Although various biological reaction systems, also called bio-reactors, could be utilized, the reaction system according to the invention preferably uses a system operating in accordance with the principle of high cell density fermentation with maximum bio-concentrations of 30 g/l in contrast to the maximally 5 g/l concentration used in conventional systems.
Preferably, the wastewater to be treated is pre-filtered before it is admitted to the reaction system, that is, it is preferably first mechanically cleaned. In this way, larger particles are removed, whereby the wastewater can be better digested by the microorganisms.
In order to provide the oxygen required for the biological digestion, air or oxygen is admixed to the wastewater in such a way that mixers or other mechanical devices are not necessary.
The wastewater, which has been treated in the reaction system often has a temperature, which is different from the operating temperature of the membrane separating apparatus. A membrane separating apparatus and also the biological pretreatment have certain optimal operating temperatures, where the separation efficiency and the biological digestion are highest. It is therefore advantageous to adjust the temperature of the wastewater before treatment.
As the membrane apparatus requires for the separation of the wastewater into a permeate and a retentate a predetermined uniform wastewater pressure at the entrance to the membrane apparatus (feed pressure), the wastewater is pressurized before it is supplied to the membrane apparatus.
The air or oxygen introduced into the reaction system preferably has a pressure of 1 to 1.2 bar, that is, it may be supplied at atmospheric pressure or at an excess pressure of 0.2 bar above atmospheric pressure. Basically however, other pressures may be selected for the oxygen admitted to the reaction system.
Depending on the amount of the wastewater supplied to the treatment apparatus, permeate may be re-circlated if the level of the wastewater (originally wastewater and retentate) in the reaction system reaches a lower predetermined limit. The permeate is discharged for consumption, when the level of the wastewater (originally wastewater, retentate and permeate) in the reaction system reaches an upper limit. The determination of the upper and lower limits is automated thereby eliminating the need for a manual switching. Manual switching may be disadvantageous for the quasi-continuous process as it may not be precise enough.
In order to avoid the need for flushing the membrane separating apparatus, which is normally necessary periodically, that is in order to operate the membrane apparatus in a quasi-continuous manner, at least a part of the retentate and/or the permeate is returned to the membrane sepa
Günther Ing Ralph
Heine Wilhelm
Loettel Ing Wolfgang
Bach Klaus J.
Rochem RO Wasserbehandlung GmbH
Upton Christopher
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