WASTEWATER TREATMENT APPARATUS AND METHOD

Abstract

A method and apparatus for the treatment of wastewater. The method comprising receiving wastewater into a tank via a wastewater inlet, evaporating a fraction of the wastewater and thereby forming a concentrate, evaporating volatile organic compounds (VOCs) out of the wastewater, collecting the VOCs thereby evaporated, and processing the concentrate, said processing typically comprising anaerobic digestion and/or thermal hydrolysis of organic compounds contained within the concentrate.

Claims

1. A method for treating wastewater, the method comprising receiving wastewater into a tank via a wastewater inlet, heating the received wastewater in the tank, thereby evaporating water and evaporating volatile organic compounds (VOCs) out of the wastewater, and thereby forming a concentrate, the method further comprising collecting the evaporated VOCs and processing the concentrate, said processing comprising anaerobic digestion.

2. The method according to claim 1 further comprising heating and/or thermal hydrolysis of the wastewater and/or the concentrate and/or sludge.

3. The method according to claim 1 wherein the evaporation comprises vacuum evaporation.

4. The method according to claim 1 wherein vacuum evaporation comprises generating water vapour and the method comprises causing heat exchange from the water vapour to subsequent influent batches of wastewater received into the tank.

5. The method according to claim 1 wherein the anaerobic digestion comprises the production of biogas, optionally biogas comprising at least 50% methane, and/or collection of the biogas.

6. The method according claim 5 wherein the method further comprises combustion of the biogas in a cogenerator, thereby producing energy and optionally using the energy generated to provide power for the method.

7. The method according to claim 1 wherein the anaerobic digestion is two-stage anaerobic digestion, comprising a first stage and a second stage, the first stage comprising hydrolysis of the concentrate and/or acidogenesis and/or acetogenesis and the second stage comprising methanogenesis.

8. The method according to claim 7 wherein the method further comprises a thermal hydrolysis step carried out on organic matter after the first stage and before the second stage.

9. The method according to claim 1 wherein the method further comprises causing the VOCs to be captured by a gas collector and/or supplied to a gas chromatograph (GC) and optionally thereby separated into distinct, individual compounds.

10. The method according to claim 1 wherein the method further comprises regulating the flow of received wastewater.

11. An apparatus for treating wastewater, the apparatus comprising a wastewater inlet, a controller, a gas collector, an anaerobic digester, at least one heating means at least one tank and at least one vacuum pump, the at least one tank comprising at least one tank inlet and at least one tank outlet; wherein the heating means and/or the vacuum pump are configured to cause evaporation of the contents of the tank, the gas collector being configured to collect volatile organic compounds, where present, thereby evaporated from the contents of the tank.

12. The apparatus according to claim 11 further comprising a generator, optionally a cogenerator.

13. The apparatus according to claim 11 wherein the gas collector comprises a gas chromatograph (GC) and/or a plurality of VOC collection containers.

14. The apparatus according to claim 11 wherein the apparatus further comprises a conduit through which wastewater and/or concentrate may flow into the anaerobic digester.

15. The apparatus according to claim 11 wherein the apparatus further comprises flow regulation means, the flow regulation means optionally comprising a pump.

16. The apparatus according to claim 11 wherein the anaerobic digester is a two-stage anaerobic digester, the two-stage anaerobic digester comprising a first digestion chamber and second digestion chamber at least partially separated from the first digestion chamber.

17. The apparatus according to claim 16 wherein the anaerobic digester further comprises a thermal hydrolysis chamber.

18. The apparatus according to claim 11 wherein the apparatus further comprises a plurality of sensors, the or each sensor comprising one or more pH sensors, flow meters, temperature sensors, pressure sensors and/or nitrogen sensors.

19. The apparatus according to claim 13 wherein the GC comprises a large scale preparative GC, the GC further comprising a GC-inlet, a GC outlet and a column, the column comprising a stationary phase and a carrier gas.

20. The apparatus according to claim 11 wherein the apparatus further comprises one or more gas purifiers.

21. The apparatus according to claim 11 wherein the apparatus further comprises one or more gas sensors configured to detect one or more gases outside the apparatus.

22. The apparatus according to claim 11 wherein the apparatus further comprises comprise an external housing, the external housing configured to retain the or each tank, digester, controller, gas purifier, gas storage chamber, GC, VOC collection container, and/or generator, wherein the wastewater inlet extends through an external wall of the external housing.

23. The apparatus according to claim 11 wherein the apparatus is plumbed into the mains water supply and/or is electrically connected to the mains electricity supply and/or is connected to the mains gas supply.

24. The apparatus according to claim 11 wherein the apparatus further comprises one or more anaerobic microorganisms.

25. Digestate and/or VOCs obtained as a result of the method according to claim 1 and/or through the use of the apparatus.

Description

DESCRIPTION OF THE DRAWINGS

[0086] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0087] FIG. 1 is a diagram of an example embodiment of a wastewater treatment apparatus according to the invention;

[0088] FIG. 2 is a diagram of a traditional wastewater treatment facility using the Activated Sludge (AS) system, as is known in the art;

[0089] FIG. 3 is a flow chart showing the main stages of one embodiment of the method;

[0090] FIG. 4 is a diagram of a combined heat and power generator; and

[0091] FIG. 5 is a diagram of an example of equipment for use in the recovery of VOCs using a gas chromatograph (GC).

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

[0092] With reference to FIG. 1, in one example embodiment of the invention a wastewater treatment apparatus (1) has a vacuum evaporation tank (2), a two-stage anaerobic digester (4), a wastewater inlet (6), a first conduit (8) through which concentrate can flow, a second conduit (10) through which concentrate can flow from a first digestion chamber (20), into a thermal hydrolysis chamber (21) and a third conduit (11) through which concentrate and/or hydrolysed sludge can flow into a second digestion chamber (22). The vacuum evaporation tank (2) also has a heater (18), and a gas outlet (24) via which VOCs and water vapour can leave the evaporation tank (2). The vacuum evaporation tank also has a vacuum pump (12). Volatile organic compounds (VOCs) that leave the tank (2) via the gas outlet (24) are directed to the gas collector in the form of a gas recovery unit (26). The gas recovery unit (26) includes a gas chromatograph and several VOC collection containers (see FIG. 5). The vacuum evaporation tank (2) also has a heat exchanger (114) with a water vapour inlet (13) and a condensed water outlet (14). In use, hot water vapour enters the heat exchanger via the water vapour inlet, and heat from the hot water vapour increases the temperature of the contents of the evaporation tank (2), thus cooling and condensing the hot water vapour, which can then leave via the condensed water outlet (14) and is discharged to the mains water supply or to a river. The two-stage anaerobic digester also has an outlet (16) through which biogas is supplied to a gas purifier, and subsequently to a gas collection chamber and finally to a cogenerator (100). The cogenerator (100) is used to supply energy both to the apparatus and to the grid. The apparatus (1) also has a controller (28).

[0093] While in the example illustrated in FIG. 1, only one vacuum evaporation tank (2) is shown, typically more than one vacuum evaporation tank (2) would be provided and each vacuum evaporation tank (2) would be supplied with wastewater for treatment. In which case, the wastewater would be treated in a batch process. In some embodiments of the invention the wastewater would be treated in a semi-continuous batch process.

[0094] This is in contrast to a traditional wastewater treatment facility (30) using the Activated Sludge (AS) process as indicated in the diagram of FIG. 2. Such facilities (30) typically have an initial primary sedimentation tank where the outflow from preliminary treatment (including flow measurement, screening, comminution, and grit removal) is allowed to settle under gravity (thereby generating a primary sludge) and the effluent is passed on for secondary treatment using the AS process. The generated primary sludge is usually transferred to a thickener (e.g. a picket fence thickener) and is thereby thickened such that is has a 5-6% dry solid concentration.

[0095] The secondary stage of a traditional wastewater treatment facility (using the AS process, as is known in the art) has a water inlet (32) and an air inlet (34) which allow water and air, respectively, to enter an aeration tank (36). Sludge and wastewater (AS) move to a clarifying-settling tank (38) where the AS is allowed to settle (thereby generating a secondary sludge), leaving behind clear water which can then leave (40) the clarifying-settling tank (38) for further treatment (e.g. UV treatment) before being returned to the mains water supply. Part of the settled secondary sludge is recycled (42) and returned to the aeration tank (36) and part of the settled secondary sludge leaves the clarifying-settling tank (44), is further thickened using a centrifuge belt (to enhance settling) such that it has a 5-6% dry solid concentration and is then mixed with primary sludge in a sludge holding tank at a proportion dependent on the design of downstream sludge processing to be treated (in this example) by an anaerobic digester (48) (which leads to the production of biogas). Such treatment processes sometimes also include thermal hydrolysis of the sludge (not shown here) before the sludge is further processed.

[0096] FIG. 3 is a flow chart of the main steps of one example of the method (50). In this example embodiment of the invention, the method (50) begins when wastewater is received (52) in the apparatus (1) and thereby into the vacuum evaporation tank (2). The vacuum pump (12) and heater (18) are switched on to adjust the conditions in the tank (2), i.e. the pressure is reduced to 20 kPa, (reducing the boiling point of the VOCs and the water), and the wastewater is gradually heated (54). This causes the VOCs in the wastewater to start to evaporate (56) (note that each distinct individual compound of the VOCs will evaporate at a different temperature and pressure). The VOCs leave the tank (2) via the gas outlet (24) of the vacuum evaporation tank (2) and are collected (58) (in the example embodiment of the invention illustrated in FIG. 1, the VOCs would be supplied to the gas recovery unit (26)). The VOCs can then leave (60) the apparatus (1). At 60 C. the water also starts to evaporate (62). The water vapour is collected, compressed (thereby increasing its temperature) and recycled for use at various stages of the method (50), e.g. for providing heat for thermal hydrolysis and/or to subsequent batches of incoming wastewater in the vacuum evaporation tank or tanks. The water vapour is then condensed and allowed to leave (64) the tank (2) via the water outlet (14) and can then be returned to the mains water supply or discharged to a river or nearby body of water.

[0097] By removing the VOCs and a portion of the water vapour a concentrate is produced. The next step of the method (50) involves processing (68) of the concentrate, in this example by anaerobic digestion. In this example, the anaerobic digestion takes place in two stages (i.e. it is two-stage anaerobic digestion) however, it will be appreciated that a single anaerobic digestion stage may alternatively be used. The first stage of anaerobic digestion involves microbial hydrolysis, acidogenesis and acetogenesis of the concentrate. The concentrate is then thermally hydrolysed. Thermal hydrolysis of the concentrate at this point allows any cellular material (e.g. from the microbial hydrolysis, acidogenesis and acetogenesis, as well as long chain fatty acids) to be broken down, thereby generating a sludge. Thermal hydrolysis ensures that the sludge is more soluble than it would be without the inclusion of the thermal hydrolysis step.

[0098] The sludge then undergoes the second stage of anaerobic digestion. The second stage of anaerobic digestion involves methanogenesis (the sludge is suitable for being readily taken up by methanogenic archaea as a result of the preceding thermal hydrolysis, the thermal hydrolysis also having reduced the potential for microbial competition and the frequent system perturbations that are common to methanogenic archaea). During the second stage of anaerobic digestion, the conditions within the second digestion chamber are controlled in response to measurements recorded by sensors which monitor the quality and quantity of sludge received from the thermal hydrolysis tank (including the acid concentration) and the accumulation of volatile fatty acids (VFAs) is thereby limited.

[0099] The anaerobic digestion produces biogas which leaves (70) the anaerobic digester (4) via the outlet (in the example embodiment of the invention illustrated in FIG. 1 the biogas would then be supplied to the cogenerator (100) where it would be combusted in order to supply energy to the apparatus). The anaerobic digestion also produces digestate (i.e. sludge). When the anaerobic digestion is complete the digestate (i.e. sludge) is removed (72) from the anaerobic digester.

[0100] This process leads to high degradation of the biodegradable substances fed into the anaerobic digester, resulting in a high volume of biogas being produced and a low volume of sludge being produced. The resultant digestate is suitable for use as a soil enhancer (as it is free from contaminants including VOCs and compounds that are produced during aerobic digestion) and can be applied directly to soil (e.g. as a fertiliser) or dried and stored for future use.

[0101] Note that in the example embodiment of the invention illustrated in FIG. 3, evaporation of wastewater and VOCs and collection of VOCs occur sequentially. In other example embodiments they may occur in a different order or simultaneously. In some example embodiments of the invention the method illustrated in FIG. 3 is carried out in several tanks (2) simultaneously, in which case each step of the method may be carried out in each tank (2) at the same time as it is carried out in each other tank (2), however it is more likely that each step of the method will be carried out in each tank (2) asynchronously.

[0102] FIG. 4 is a diagram of a cogenerator (a combined heat and power (CHP) generator) (100). The cogenerator has an inlet (102) through which biogas is supplied. The inlet (102) leads to a combustion engine (104) where the biogas is combusted. The combustion engine (104) is connected to an electricity generator (108) driven by the drive shaft (106) of the combustion engine (104). The exhaust heat from the combustion engine (104) is supplied to a heat exchanger (112). Cold water (120) is supplied to the heat exchanger (112) and picks up heat from the exhaust gas (122) that results from combustion of the biogas. The water (120) leaves the heat exchanger (112) at a higher temperature and (in this example) is supplied directly to a radiator (114), although it should be understood that it may instead be supplied to a central heating system, for example. The exhaust gas (122) is supplied to a catalytic converter (116) which removes some compounds from the exhaust gas. The exhaust gas then leaves the cogenerator via the exhaust pipe (118).

[0103] Referring to FIG. 5, the GC is connected to the vacuum evaporation tank (2) and a water vapour outlet (172). The GC has a gas injector (150) where the gases are periodically mixed with the carrier gas before they are injected into the gas column (152). The gas column (152) is made of stainless steel and is packed with the stationary phase (one skilled in the art will appreciate that the gas chromatograph may have multiple columns and that the choice of stationary phase and carrier gas will depend on the target VOCs.) The gas column (152) is heated by fluid circulating in a jacket around the column (152) to maintain the carrier gas and the injected VOCs at a constant temperature. The GC also has a thermal conductivity detector (154), several selection valves (156) that allow selected VOCs to collect in several VOC condensers (158), several gas-liquid separators (160) and a pump (162) arranged such that individual, distinct VOCs may be removed from the GC. The GC also has a carrier gas cleaner (164), a carrier gas compressor (166) and a carrier gas heater (168). In use, the retention time of target analytes (e.g. individual, distinct VOCs) would be pre-programmed into the controller (28) and these analytes (VOCs) are detected by the detector (154) as they elute from the column (152). In response to the detection of a given analyte (VOC), the controller causes a selection valve (156) to open (note that only one valve (156) is open at any given time). Subsequent cooling of the mixture of carrier gas and vaporised analyte (VOC) result in the vaporised analyte condensing out of the carrier gas. The carrier gas is then physically separated from the condensed (liquefied) sample by the gas-liquid separators (160) and is recycled while the recovered analyte (VOC) is directed to an appropriate VOC collection container (170).

[0104] Any traces of VOCs are removed from the carrier gas by the carrier gas cleaner (164) (the carrier gas cleaner in this example is an activated charcoal bed). Then the carrier gas is compressed by the carrier gas compressor (166) and is heated by the carrier gas system (in this example to 80 C.).