WO1992002465A1

WO1992002465A1 - Treatment of a trickling-percolating filter

Info

Publication number: WO1992002465A1
Application number: PCT/GB1991/001271
Authority: WO
Inventors: Frank L. Horsfall, Iii
Original assignee: Biosphere Corporation S.A.; Secopro International Limited
Priority date: 1990-07-27
Filing date: 1991-07-26
Publication date: 1992-02-20
Also published as: GB9016505D0; CA2066231A1; AU8301991A

Abstract

A method of treatment of a trickling-percolating filter to remove or inhibit blockages which consists in feeding electron acceptor substances (nitrates) with the filter medium in a distributed fashion. Perforated pipes (5) may be sunk into the filter medium (2) for the application of the substances in liquid form. The application of the electron acceptor solution may be followed by the application of a liquid suspension of bacteria capable of using the said solution.

Description

TREATMENT OF A TRICKLING-PERCOLATING FILTER

The invention relates to a method of treatment for the restoration and maintenance of the function of a trickling-percolating filter for wastewater and provides a specially developed application system used with the process equipment available on-site at the wastewater treatment plant.

This system provides an extremely economic restoration process for existing trickling-percolating filters which have restricted flow and would, under the circumstances, require disassembly, cleaning and reassembling for rectification. The method can be utilised while the filter is operating or after the filter has become blocked and is no longer operational. The system described also provides for on-line maintenance while the trickling-percolating filter continues to function.

Among the various types of wastewater treatment plants, there are those that have trickling- percolating-filters as part of their operating processes. A trickling-percolating filter is a fixed medium secondary system. The medium is composed of tightly packed material, usually stones, sheets of Neoprene rubber or plastic shapes of various types, usually contained in a cylindrical tank. The medium provides a surface on which a microbial mass develops as a result of the utilisation of the food e -\ά nutrients present in the influent wastewater by microorganisms. The wastewater is distributed over the surface of the medium usually by means of rotating arms. Thus the wastewater is allowed to trickle over and percolate through the medium. It is therefore cleaned by the action of the microbial mass growing on the medium. The process of cleaning the wastewater is usually aerobic, requiring oxygen from the air present in the interstitial spaces in the medium. The oxygen provides the oxidizing potential to the growing microbial mass, or biomass, growing there. During this growing process solids are produced which must exit the filter. Usually these solids are sloughed from the medium and collected in the secondary clarifier of the treatment plant. When all these processes take place uniformly and consistently, the trickling-percolating filter functions effectively.

There are times, however when the growth of the microbial mass produces excessive solids which may form bridges between and among the pieces of the medium. This growth prevents continued flow of the influent wastewater through the filter and thereby hinders the operation of the filter. If the excessive growth is severe enough, it can completely restrict the flow of wastewater through the filter and liquid build-up will occur on the surface of the medium. This condition is called "puddling/ponding" and results in a totally ineffective filter.

The usual remedy for "puddling/ponding" is to dismantle the filter and clean it physically, a very costly and time consuming process. This procedure takes the filter being cleaned out of service until it is rebuilt. Since the trickling-percolating filter is the secondary process of the wastewater treatment plant, the whole plant is limited or inoperative during the rebuilding of the filter.

According to one aspect of the invention there is provided a method of treatment of a trickling- percolating filter which consists in applying, in a distributed manner within the body of the filter medium, a liquid solution of one or more electron acceptor substances.

Preferably, the application of the electron acceptor solution is followed by the application of a liquid suspension of microorganisms (bacteria) capable of using the said electron acceptor substance or substances.

The soluble electron acceptor substitutes for oxygen which is no longer available to the biomass while a "puddling/ponding" condition remains. This technique allows an on-site and in place bio-remediation of the trickling-percolating filter. It is, in fact, a bacterial and biochemical process which restores function to the filter during the course of the treatment process itself. The technique can be continued after the filter returns to effective operation as a preventive maintenance process and to improve process treatment and capacity.

Injection of a concentrated solution of sodium or potassium nitrate salts having a concentration of 50% weight/volume or greater, for example, into the trickling-percolating filter, can be accomplished by pouring the solution into porous pipes, made of plastic or other material and placed vertically into the medium symmetrically over its surface. The bacterial suspension can, as well, DΘ poured into these same pipes. If the pipes are driven deeply enough into the medium they will not interfere with the rotation of the arms of the trickling-percolating filter. They may be left in place in the medium and used as a part of the regular maintenance program of the trickling-percolating filter. Applying the solution of concentrated nitrate salts and the bacterial suspension to the filter media in this way, at 1 to 2 litres of each liquid per pipe per application, using a weekly or monthly schedule, will preclude future "puddling/ponding" problems caused by organic solids build-up. It can also facilitate the treatment of influent wastewater by the filter during periods of high flows and/or high organic loading, as long as these conditions are of short duration.

The restoration of the filter by the biochemical bacterial system described herein involves, among the basic biochemical functions provided by the bacteria as they grow, several processes produced by the hydraulics of the newly introduced pipes and the products of the utilisation of nitrate as an electron acceptor. Normally the hydraulic pressure provided by the influent is downward. The hydraulic pressure provided by the pipes is horizontal as the liquid exits these pipes from their sides. In addition, nitrogen gas is produced from the denitrification of the nitrate by the bacteria of the system. This nitrogen gas provides an additional turbulence as it will rise vertically out of the media present in the percolating-trickling filter. Thus there are now three pressures and flows provided during the use of the described system: hydraulic, downward and lateral and gaseous upward. The technique of installation of feed pipes into the filter herein described may be incorporated into the original structure of the filter as functional improvement at the time of design and construction stage of the filter. According to another aspect of the invention there is provided a trickling-percolating filter comprising a container which holds a filter medium; a rotary arm structure arranged above the filter medium to trickle-feed wastewater on to the medium; and a plurality of spaced porous pipes embedded in the medium and adapted to be fed with liquids for remedial and/or preventative blockage treatment of the medium, the pipes being effective to feed the liquids in distibuted fashion throughout the medium.

The invention will further be described with reference to the accompanying drawings, of which:-

Figure 1 is a top view of a filter incorporating the invention;

Figure 2 is a cross-sectional view of the filter of Figure 1.

Figure 3 is a diagram illustrating the manner in which the perforated pipes are inserted into the filter medium.

Referring to the drawings the filter 1 comprises a medium which is a bed of granular material 2 comprising stones, plastic shapes etc. which fills a cylindrical tank 3. A set of rotating perforated arms dispenses wastewater onto the top of the bed. The wastewater trickles through the medium and is aerobically treated by bacteria therein.

The invention provides a set of vertical perforated pipes 5 plunged into the material which can be connectedto a fluid supply system (not shown) . Periodically, or as required, fluid comprising a solution of sodium or potassium nitrate salts is fed to the pipes 5 bypassing and removing blockages which may cause "puddling/ponding" . The pipes 5 are also used for the distribution of liquid containing specific microorganisms which are prescribed to provide the biological activity needed to release blockage of the medium material by utilising the nitrate salts and to enhance the action of the filter.

Examples of specific solutions found to be effective both in constitution and concentration:

50% solution of Sodium Nitrate or 50% solution of Potassium Nitrate

The time interval between the application of the nitrate solution and the bacterial suspension is approximately 1 to 2 hours.

Example of suitable bacterial suspension:

SPECIES

BACILLUS 2-4

ENTEROBACTER 1

PSEUDOMONAS 2

AGROBACTER 1

NITROSOMONAS 1 NITROBACTER 1

TOTAL 5000 cells/ml Figure 3 shows a system for the installation of the feed pipes into a filter medium of the filter. In situations where the filter medium is tightly packed or compacted it is necessary to create open vertical shafts into the filter medium by means of a mechanical device which can penetrate to the base of the medium for the purpose of inserting the feed pipes.

An example of such a system is one that includes three 3 parts. First, a drill tip/pipe anchor 12. Second, a hollow driving shaft 12 having a pair of handles 13 mounted at the upper end. Third, a suitable pneumatic hammer 14. The three pieces fit together as follows: The drill tip/pipe anchor is inserted into the base of the hollow driving shaft until contact is made with a stopping pin 15 mounted in the drill tip/tube anchor. These two pieces are then held vertically at the point on the filter bed where the feed pipe is to be located. The pneumatic hammer then drives the hollow driving shaft with the inserted drill tip/pipe anchor into the filter medium to the desired depth. Several different lengths of hollow driving shafts may be required depending on the depths of the filter medium encountered. Upon reaching the desired depth, the pneumatic hammer is withdrawn from the hollow driving shaft. A feed pipe is then inserted into the hollow driving shaft until it contacts the drill tip/pipe anchor. The hollow driving shaft is then withdrawn leaving the feed pipe in place at the desired d -»th. The feed pipes do not extend above the level of the medium sufficiently far to impede the rotation of the feed arms. The top of the feed pipes may be marked for easier location and identification.

Claims

1 A method of treatment of a trickling-percolating filter which consists in applying, in a distributed manner within the body of the filter medium, a liquid solution of one or more electron acceptor substances.

2 A method as claimed in claim 1 wherein the electron acceptor substances comprise nitrates of potassium and/or sodium.

3 A method as claimed in claim 1 or claim wherein, in addition to the application of the electron acceptor substance or substances, there is applied, in a distributed manner within the body of the filter medium, a liquid suspension of microorganisms capable of using the said electron acceptor substance or substances.

4 A method as claimed in any of the preceding claims wherein the said distributed application within the body of the filter medium is effected by means of porous or perforated pipes driven through the medium.

5 A method as claimed in claim 4 wherein the pipes are permanently in place and said treatment is remedial, being made as required to remedy blockages or partial blockages of the filter medium.

6 A method as claimed in any of the claims 1 to 4 wherein the pipes are permanently in place and said treatment is preventative, being made regularly to inhibit blockages forming.