EP1084083A2

EP1084083A2 - Filtering plant for waste water

Info

Publication number: EP1084083A2
Application number: EP19990943497
Authority: EP
Inventors: Nils Erik Pedersen; Lars Westlie
Original assignee: Jordforsk
Current assignee: Jordforsk
Priority date: 1998-06-12
Filing date: 1999-06-10
Publication date: 2001-03-21
Also published as: NO307653B1; WO1999067173A3; NO982737L; NO982737D0; AU5657299A; CA2334829A1; WO1999067173A2

Abstract

This invention comprises a purification plant for purifying waste water and recycling water from a small group of households, agricultural units, cabins and the like. If the plant receives only grey water, the plant should purify it to such an extent that the water can be re-used for watering, washing, flushing of toilets, etc. If the plant receives black water, the plant should purify it to such an extent that the effluent can be safely discharged into the environment. The plant is divided into three main parts; a sludge interceptor, a main filter with vertical unsaturated aerobic flow at the top and saturated anaerobic flow at the bottom of the filter, and a final filter with horizontal saturated anaerobic flow. As a final treatment the water is disinfected in order to remove bacteria. The filter plant is equipped with one or more buffer zones and overflow pipes between the main parts in order to give the plant the capacity to absorb extraordinary loads without untreated waste water running out into the environment.

Description

Filtering plant for waste water

This invention relates to a purification plant for purification of waste water and recycling water from a small group of households, agricultural units, cabins and the like. If the plant receives only grey water, the plant should purify it to such an extent that the water can be re-used for watering, washing, flushing of toilets, etc. If the plant receives black water, the plant should purify the water so that it can safely be discharged into the environment. The plant is divided into three main parts; a sludge interceptor, a main filter with vertical unsaturated aerobic flow at the top and saturated anaerobic flow at the bottom of the filter, and a final filter with horizontal saturated anaerobic flow. As a final treatment the water is disinfected in order to remove bacteria. The filtering plant is equipped with one or more buffer zones and overflow pipes between the main parts in order to give the plant the capacity to absorb extraordinary loads without untreated waste water running out into the environment. The term aerobic means with access to external oxygen, while anaerobic means without access to external oxygen.

Background

Local conditions may give rise to various problems associated with water consumption in households, agricultural units, cabins and the like. In some urban areas and other areas with high population density, e.g.. the water resources may be limited, thus making it desirable to use the water several times for different purposes, while in sparsely populated districts it is often expensive and impractical to build municipal/regional waste and purification plants for the waste water. If in addition the local ground conditions have a low drainage tolerance, earth filters and similar solutions will not constitute a suitable purification method for the waste water. In these cases a purification plant may be an acceptable solution.

Waste water contains biological and chemical components such as bacteria, phosphorus, nitrogen and organic materials, etc. These can cause local pollution problems such as acidification, dissemination of disease, overfertilisation of streams and water and the like if the waste water is discharged freely into the environment. When municipal/regional waste water facilities are not present, therefore, the waste water should be treated in order to reduce the content of, or completely remove, these components in order to ensure that the environment does not receive excessive amounts of the waste water's content of infectious and/or other environmentally hostile substances. In those cases too where the water resources are scarce and the waste water is required for watering, washing, flushing toilets, etc. in order to reduce the household's water consumption, the waste water should be purified before re-use.

Prior art

The use of sand and other filter materials in a reservoir is known for purification of waste water where the water is dispersed on and/or in the filter media and transported through the filter media. In such filters it is known to perform the purification under either anaerobic conditions, e.g. the filter medium is saturated with water, or under aerobic conditions where the filter medium is not saturated with water. There are many different devices and filter materials for such filters, but they will not normally combine zones with purification under both saturated and unsaturated conditions or have the possibility of regulating the size of the different zones for optimisation of the purification process.

In EP 0 654 015 a purification plant is disclosed which has combined a sludge interceptor with aerobic conditions, a second reservoir with anaerobic conditions filled with active carbon and mineral filter medium and a third reservoir with aerobic conditions where the water flows through a series of filter walls filled with active carbon or mineral filter medium. Part of the water will be recirculated back to the sludge interceptor. This plant, however, is not equipped with buffer zones which enable the plant to absorb extraordinary loads, nor has it the possibility of regulating the ratio between the size of anaerobic and aerobic zones in the plant.

The object of the present invention

An object of the present invention is to provide a compact purification plant which can purify grey water chemically, mechanically and biologically under both aerobic and anaerobic conditions, from a small group of households, agricultural units, cabins and the like to such an extent that the water can be re-used for watering purposes, as washing water, for flushing of toilet bowls. etc. If the waste water also contains water from the toilet, so-called black water, the plant should purify the water to such an extent that it can safely be discharged into local earth masses or another recipient without the risk of local pollution.

It is also an object of the present invention to provide a purification plant which has a large buffer capacity in order to be able to absorb substantial extraordinary loads without the risk of untreated waste water evading the purification process, with the result that the risk of sludge escaping from the plant is as good as eliminated.

Another object of the invention is to provide a purification plant which can easily regulate the recirculation of the water between the different purification zones, the water's residence time and where it is easy to replace filter media, thus providing the plant with a very high total purification effect which satisfies present day requirements for purification of phosphorus, organic materials, nitrogen and bacteria by a wide margin.

A further object of the present invention is to provide a purification plant which is optimised with regard to nitrogen removal, and which can rapidly be adjusted/modified in order to maintain optimal nitrogen removal without conversion or alterations to the filter medium according to any changes in the operating conditions.

Description of the invention

The objects of the invention are achieved with a purification plant consisting of several well-tried filtering techniques which are assembled in a specific combination: Sludge interception with denitrification and prefiltering, dispersal of water over a main filter medium for purification under aerobic unsaturated conditions, followed by purification in a final filter medium with saturated anaerobic conditions and finally disinfection by means of UV radiation or another disinfection method, such as sodium hypochlorite, ozone, etc. In addition both the sludge interception chambers and the final filter are equipped with buffer zones and connected to each other by one or more overflows in order to ensure that non-disinfected water does not escape during periods of extraordinary loading of the plant. The sludge interceptor removes suspended materials and is divided into three chambers, two sedimentation chambers and a coarse prefilter. The sedimentation chambers are designed in such a manner that they have a large volume and so that the water is forced to take a long path. The sedimentation chambers should preferably be designed in such a manner that the water is forced to make a 180° turn in order to enter the second sedimentation chamber. This increases the residence time and thereby the sedimentation in the first sedimentation chamber. The removal of suspended material is further ensured by the fact that the sludge interceptor has a prefilter. The prefilter will form a biofilm which removes some of the content of organic material and bacteria in the waste water while some of the phosphorus content will be chemically bound to the filter medium. The first sedimentation chamber is also used for denitrification of water recirculated from the main filter.

After sludge interception the water will be pumped into a dispersal system which comminutes the water on the upper surface of the filter medium in the main filter in such a manner that the water will be passively enriched with oxygen. Passively means without the injection of air into the filter. In the main filter the water will undergo purification under vertical unsaturated aerobic flow conditions as it percolates downwards in the filter medium. In this process phosphorus will be chemically bound to the filter medium by means of adsorption, organic material is removed mechanically and bacterially by means of an active bioskin, and the nitrogen content of the water will be nitrified into nitrations. Bacteria will also be retained in the filter medium. This is the largest filter, and the size will cause this step to represent the principal purification of organic material, phosphorus and bacteria. In the bottom of the main filter there is located a collecting pipe which passes water to a pump chamber. The height of the collecting pipe's outlet can be adjusted, thus causing a water surface to be formed in the lower part of the main filter. The bottom part of the filter medium thereby becomes saturated with water, thus creating anaerobic conditions in this area. Under anaerobic conditions the nitrations will be converted bacterially to nitrogen gas (denitrification), while the removal of organic material, bacteria and phosphorus will be conducted at approximately the same rate as for the aerobic part of the filter. The height adjustment of the water surface allows the ratio between aerobic and anaerobic filter media to be adjusted by a simple movement for optimisation of the nitrification and denitrification processes.

As mentioned above, after having passed through the main filter, the water is transported in a perforated pipe which is placed along the bottom of the filter to a pump chamber. The pump will pass some of the water back to the first sedimentation chamber for denitrification and the rest to the final filter for final purification via a distribution pipe. The distribution of the water between the final filter and the sludge interceptor can easily be adjusted by means of valves mounted on the distribution pipe. In the final filter the water will pass horizontally through the filter medium under anaerobic saturated conditions, thus causing the water to be denitrified. The final filter will also remove residual organic material, bacteria and phosphorus.

The object of recirculating some of the water from the main filter back to the first sedimentation chamber is to utilise the high incidence of carbon in the chamber for the denitrification process. It is well known that carbon is necessary for the denitrification process, and an area with a high incidence of carbon will therefore enhance the removal of nitrogen in the plant. In addition there are two other zones in the plant which also contribute to the removal of the nitrogen content. This gives the plant a very high total purification effect on nitrogen.

After the water has passed through the final filter it is passed through a disinfection unit for further removal of bacteria. The water is then discharged into local earth masses or another water recipient, or collected in tanks for reuse.

The plant is designed to be able to accept a larger volume of water than that which is the average water consumption per day for the user units. This is due to the fact that the plant has a fixed through-flow area on the throughput connections between the different chambers. However, both the sludge interceptor and the final filter can increase the water level in order to absorb sudden extra loads if the plant is loaded with more water than that which can run through the throughput connections per time unit. Even though the water level rises, however, all the water will still pass through the filters, thus creating buffer zones. In addition a guarantee is obtained that if the water level rises too much in the sludge interceptor an overflow will pass the water to the pump chamber for the main filter, while for the final filter chamber a second overflow will pass water back to the sludge interceptor if its buffer zone is exceeded. A guarantee is thereby obtained that the entire plant will absorb extra loads before untreated water will escape. This gives the plant a very large total buffer zone, thus essentially eliminating the risk that sludge and/or untreated water will escape.

The plant has three chambers which employ filter media. Any kind of material may be employed which satisfies the requirements regarding permeability, porosity, specific surface, ability to form bioskin and the capacity for binding phosphorus given in Table 1. No requirements are placed on the bottom and the wall materials of the plant apart from the fact that they have to be capable of withstanding water and the pressure conditions in the plant, both externally and internally.

Examples of preferred embodiments

The invention will now be described in more detail with reference to two examples of preferred embodiments of the purification plant and with reference to the accompanying drawings of the embodiments.

Figure 1 is a plan view seen from above of a first preferred embodiment of the purification plant according to the invention. The arrows indicate the direction of flow of the water.

Figure 2 is a side view of the first preferred embodiment illustrating the second sedimentation chamber and the prefilter chamber.

Figure 3 is a new side view of the first preferred embodiment illustrating the prefilter chamber and first pump chamber. This view is perpendicular to the view presented in figure 2.

Figure 4 is an interrupted side view of the main filter, second pump chamber and first sedimentation chamber in the first preferred embodiment.

Figure 5 is a side view of the final filter and the UV unit in the first preferred embodiment.

Figure 6 is a plan view seen from above of a second preferred embodiment of the plant according to the invention. Example 1: First preferred embodiment

From figure 1 it can be seen that the first preferred purification plant is rectangular and composed of 7 chambers. The first sedimentation chamber is indicated by reference numeral 1 , the second sedimentation chamber by 2, the prefilter chamber by 3, the first pump chamber by 4, the main filter chamber by 5, the second pump chamber by 6, the final filter chamber by 7 and the UV chamber with outlet by reference numeral 8.

Table 1 : Preferred requirements for filter materials

Chamber Phosphorus binding Permeability Structure^)

Prefilter No requirements > 1 500 m/day 4 - 20 mm

Main filter > 5 kg/m³ > 100 m/day 0.25 - 7 mm

Final filter > 5 kg/m³ > 1 000 m/day 0.25 - 7 mm

1 ) The shape of the filter material can be both round or angular. The first sedimentation chamber has a wet volume of l .όm^ (wet volume refers to the amount of water in the chamber at lowest normal water level). Waste water enters the chamber through inlet 1 1. flows through the chamber and on into the second sedimentation chamber 2 via a 1 10 mm transition pipe which is located in the middle at 2/3 the height (measured from the bottom) on the short partition between the sedimentation chambers (not shown). The chamber is designed in such a way that the water has to make a 180° turn before entering the second sedimentation chamber. As mentioned, water from the main filter will be returned to the first sedimentation chamber for denitrification. This is carried out by means of a perforated pipe 66 which distributes and mixes water from the second pump chamber 6 with the water in the chamber (see also figure 4).

The second sedimentation chamber 2 has a wet volume of 0.8 m^, and is a pure sedimentation chamber. In figure 2 it can be seen that the water flows out of the chamber through a 110 mm transition pipe 21 which is located at 1/3 of the height from the bottom. The transition pipe 21 is located at the opposite end of the chamber relative to the transition pipe between chambers 1 and 2, and is connected to a vertically perforated 75 mm distribution pipe 31 which is located in the prefilter's filter medium. The distribution pipe 31 will distribute the water over the entire height of the filter medium. In the event that the perforation should be clogged by suspended material, the distribution pipe 31 is extended so that it reaches higher than the filter medium and is equipped with an overflow 33. In the figure the water level in the event of maximum utilisation of the buffer volume is indicated by the arrow 32.

The prefilter chamber 3 has a wet volume of 0.8 m , and is filled with a filter medium consisting of Leca Lettklinker (light clinker) or a similar material with a diameter of 4-20 mm. The water will flow horizontally through the filter medium under anaerobic saturated conditions. After the water has passed through the filter it will be collected in a 75 mm perforated collecting pipe 34 which flows into the first pump chamber 4 (see figure 4). The end of the collecting pipe 34 may be equipped with transitional end pieces 35 in order to regulate the water through-flow. This offers the possibility of increasing the water's residence time in the sludge interceptor and thereby increasing the sedimentation and denitrification. In periods of extraordinary loading the water level in the sludge interceptor will rise. In order to prevent flooding, the partition between the prefilter chamber and the first pump chamber is equipped with a 1 10 mm overflow 36 immediately above the water level which corresponds to the maximum utilisation of the buffer volume.

The water level in the sludge interceptor may be increased by 15 cm, which corresponds to a buffer volume of 330 1.

After the prefilter chamber the water enters a first pump chamber which is equipped with a float switch-controlled pump 41 which will intermittently pass water into a dispersal system 51. The dispersal system distributes the water over the main filter's 54 upper surface (see figure 1 ). The float switch has been given reference numeral 42. The chamber has an area of 0.50 m x 0.35 m. The main filter consists of Leca Lettklinker (light clinker) or a similar material with a diameter of 1-4 mm and has an area of 5 m^. The dispersal system 51 consists of a rectangular pressure pipe equipped with five spray nozzles (not shown) which will disperse the water evenly over the entire filter surface while saturating the water with oxygen. The water will percolate vertically down through the filter medium under aerobic unsaturated conditions until it meets a water surface at approximately 1/3 of the height from the bottom. From there and down to the bottom of the main filter, the water will be purified under anaerobic saturated conditions. As mentioned, the water's nitrogen content will be nitrified into nitrate under aerobic conditions, and denitrified into elementary nitrogen gas under anaerobic conditions. The main filter has the capacity to convert virtually the entire nitrogen content of the water to nitrate, but can only convert parts of the nitrate formed into elementary nitrogen. In addition the main filter has the capacity to purify around 90% of the water's content of phosphorus and organic material. After the water has passed through the filter medium, it will be collected in a 32 mm perforated collecting pipe 52 which is located diagonally along the bottom of the main filter and will flow into the second pump chamber 6. The end of the collecting pipe 52 is in the form of a gooseneck 53 (see figure 4). The gooseneck can be rotated about the attachment point of the collecting pipe, thus enabling the height of the discharge point on the gooseneck to be raised and lowered in order to alter the height of the water surface, thus permitting the ratio between the aerobic and anaerobic zones in the main filter to be adjusted according to requirements.

As mentioned, water which enters the second pump chamber 6 will contain a large amount of nitrations. In order to exploit the favourable conditions for denitrification in the sludge interceptor, some of the water is recirculated back to the first sedimentation chamber by a float switch-controlled pump 61 passing water into a double-branched pipe 63 which is connected at one end to a perforated lead-in pipe 66 in the sedimentation chamber (see figures 1 and 4) and at the other end to a vertical distribution pipe in the final filter.

The volume of water which is recirculated to the first sedimentation chamber can be easily regulated by means of valve 65. In order to achieve the best possible purification effect, as much water as possible should be recirculated to the first sedimentation chamber, but of course there must be a balance between ingoing and outgoing water in the plant.

In order to further increase the plant's denitrification capacity and to ensure that phosphorus and organic material are adequately removed, the remainder of the water entering the second pump chamber 6 is passed to a final filter 7 for post-purification via the second branch of pipe 63 which is connected to a 75 mm perforated distribution pipe 71 which is located vertically in the final filter's filter medium 72 in a corner of the final filter chamber 7 (see figure 1). The final filter employs the same filter material as the main filter. The volume of water passed to the final filter can be easily regulated by means of a valve 64. The water will flow horizontally through the final filter's filter medium 72 to a 75 mm perforated collecting pipe 73 which is located in the opposite corner to the distribution pipe 71. As mentioned, the purification is carried out in the final filter under anaerobic saturated conditions. The collecting pipe 73 is connected to an overflow 74 which passes the water to a UV unit 8 for further removal of bacteria (see figures 1 and 5). The overflow 74 is equipped with a valve 75 for regulating the volume of water which flows through the UV unit. The UV unit is connected to a submerged outlet sump 81 with outlet 82. The outlet sump 81 has the capability of sampling water (not shown). The chamber 7 has two safety overflows. In the event of extraordinary loading chamber 7 can have 10 cm extra capacity before the water will be returned by means of gravity to the first sedimentation chamber 1 via an overflow 76. This ensures a greater purification effect while at the same time utilising the buffer capacity of the sludge interceptor. If the water level in chamber 7 rises further, the water will be conveyed past the UV unit 8 and down into the outlet sump 81 via overflow 77. This may arise in the event of extreme loading, but will probably not occur. The object of the overflow 77 is to ensure that the plant obtains satisfactory operating stability. The water level in the final filter can be increased by 10 cm, giving a buffer volume of 130 1. The total buffer volume for the plant will be 460 1, corresponding to approximately 1 day's consumption for a detached house.

In order to ensure that the waste water passes through the plant as expected, the pumps in the first and second pump chambers should be equipped with an alarm in case of pump failure, and a spare pump should be available. The sedimentation chambers should be emptied of sludge once a year. The same applies to the filter medium for the prefilter. The filter medium for the main and final filters is expected to last for 5 years before having to be replaced. All materials which are watertight in the long-term and have sufficient load- carrying capacity to resist the water pressure can be employed for the plant's walls and bottom (concrete, fibre glass-reinforced polyester, etc.).

As mentioned, the plant is composed of several known purification techniques. To date no measurements have been taken of the plant's total purification effect, but full-scale tests have been carried out on individual purification steps in the plant. On the basis of these results the purification effect for the remaining steps and a total purification effect for the whole plant under optimised conditions have been stipulated, both with regard to purification of grey water and black water. The values are given in Table 2.

The stipulation is a theoretically anticipated purification effect calculated on the basis of each chamber's dimensions, process technical details, composition and design. Included in the calculation is the fact that 50% of the water in the second pump chamber is recirculated to the first sedimentation chamber. This will give a dilution effect which will be transmitted on to the other chambers. This dilution effect was not present during the measurements on the individual purification steps, with the result that the documented values in Table 2 will be slightly too high.

Example 2: Second preferred embodiment

The second preferred embodiment is constructed in a similar manner to the first preferred embodiment, but in a round shape instead of a rectangular shape. A round shape is favourable with a view to mechanical strength and production costs.

In this form the plant is composed of a circular main filter chamber 5 with the other chambers extending successively along the main filter chamber's outer wall (see figure 6). The total diameter of the plant is 4 m.

The area of the main filter is the same as the main filter in example 1 , while the base of the other chambers has a slightly different size to the corresponding chambers in example 1. As can be seen in figure 6, there is no 180° "bend" between the first and second sedimentation chambers. Otherwise the only change compared to example 1 is that the water level in the sludge interceptor can only be raised by 10 cm, thus giving a buffer volume of 316 1. As in example 1 , the water level in the final filter can be raised by 10 cm, thus giving a buffer volume of 204 1. The total buffer volume is 519 1. Table 2 Stipulated values for anticipated purification effect for the first preferred embodiment of the plant according to the invention. The stipulated values are calculated on the basis of documented¹) values from tests on single-chamber filters corresponding to individual chambers in the plant.

1 ) Documented values are taken from Jordforskrapportene (Earth Research Reports); 1 16/97, 140/97 and 144/97, and from the periodical Vann (Water) no. 1 , 1996. 2) BOF₇ is the amount of organic material measured for biological oxygen consumption and TKB is thermostable koliform bacteria.

Even though the invention is described with reference to two preferred embodiments, it should be understood that the invention is not restricted to these. Alternative designs with separate free-standing chambers, chambers of other shapes etc. are within the scope of the invention.

Claims

PATENT CLAIMS

1. A purification plant for mechanical, chemical and biological purification of waste water and grey water for re-use, from a small group of user units, characterized by the combination of: a) a pre-treatment section for the waste water, comprising two sedimentation chambers (1, 2) and prefilter (3), which work under anaerobic saturated conditions for removing suspended material, b) a main filter (5) with dispersal bodies (51), by means of which the water is dispersed over the filter surface (54) under aerobic, unsaturated conditions for conversion of the nitrogen content into nitrations and purification of organic material, phosphorus and bacteria, c) after the main filter (5) a final filter (7) with a water distribution mechanism (63), by means of which part of the water is distributed in the filter medium (7) under anaerobic saturated conditions for converting the nitrations formed into elementary nitrogen gas (denitrification) and continued purification of phosphorus, organic material and bacteria, while the other part of the water through recirculation elements (65, 66) is returned to the first sedimentation chamber (1) in order to exploit the favourable conditions for denitrification in the chamber, and d) a UV unit (8) after the final filter (7), for further removal of bacteria before the water is discharged from the plant,

- both the sludge interceptor, the first and second sedimentation chambers (1 , 2) and the prefilter (3) and final filter (7) being equipped with buffer zones in order to absorb unexpected, substantial extraordinary loads,

- the buffer zones being interconnected by means of an overflow in order to ensure that the buffer zones are utilised to the maximum before untreated water is discharged from the plant.

2. A purification plant according to claim 1, characterized in that the height of the main filter's outlet (52) can be adjusted for raising/lowering of the water surface in the filter medium (5) for regulation of the ratio between anaerobic and aerobic filter zones in the plant.

3. A purification plant according to claim 1, characterized in that it is designed for purifying grey water down to a phosphorus content of less than 0.05 mg/1, nitrogen content of less than 2 mg/1, organic material measured by BOF7 of less than 3mg/l and for complete removal of the content of thermostable koliform bacteria (TKB).

4. A purification plant according to claim 1 , characterized in that it is designed in such a manner that it can purify black water down to a phosphorus content of less than 0.8 mg/1, a nitrogen content of less than 30 mg/1, organic material measured by BOF7 of less than 15 mg/1 and the TBK content to less than 50 per 100 ml.

5. A purification plant according to claim 1 , characterized in that the flow of recirculated water to the first sedimentation chamber (1), water to the final filter (7) and water to the UV unit (8) can be regulated in order to optimise the degree of purification.