(11) Patent Number: KE 400
(73) Owner: BOlD 15/00, 21/00, C 02F 1/28, 1/463,MOl UNIVERSITY of P.O. Box 3900-30100, ELDORET, Kenya
(21)Application Number: KElP/ 2004/ 000408
(72) Inventor:ETIEGNI Lazare of Department of wood science & Technology, Moi University, P.o. Box 1125 Eldoret Kenya; Orori Ondengi Bernard of Dept. of Wood Science, Moi University, P. 0. Box 1125 Eldoret, Kenya and Rajab Said Mohammed ofMoi University, P. 0.
(22) Filing Date:07/04/2004
(30) Priority data: BOX 3900, Eldoret, Kenya.
(74) Agent/address for correspondence:
(54) Title: AN ELECTRO-COAGULATION METHOD FOR COLOR REMOVAL IN WASTEWATER OR WATER WITHLOWPOWERCONSUMPTION.
(57) Abstract: A method of treatment of wastewater or water where the wastewater/water to be treated is first mixed with wood ash at a ratio of 0.278kg of ash per m3 ( Cubic meter) of wastewater/water. The resulting wood ash leachate is first allowed to settle to remove larger debris before it is subjected to electro-coagulation to remove color. The detention time of leachate during electro-coagulation is kept at a
maximum of one minute to ensure minimal power consumption. Further to this, the ratio of electrode surface area to volume of water is kept close to 0.0645 m2/m3.
An Electro-coagulation Method of Color Removal in Wastewater or
Water with Low Power Consumption
The present invention discloses a method for removing color from industrial wastewater for discharge into rivers or to be recirculated for industrial use. The method can be extended further to apply to raw water in rivers for industrial and domestic use.
Color is a rather conspicuous occurrence as a result of industrial processes such as pulp and paper manufacture, coffee processing, textile dyeing, electroplating and a host of other industries. Unfortunately, discharge of colored industrial effluent is objectional and stringently regolated as this low quality effluent bas several sdverse impacts on the environment, especially on the rivers receiving such effluent. High color level in the VIBStewater changes the aesthetic quality and reduces light penetration of the receiving waters while potentially affecting benthic plant growth and habitat. Additionally, colored effluents result in reduced river water photosynthetic activity, increased long term BOD, increased water treatment cost for users down stream of the discharge point, and increased toxicity. Effluent color is also used as an indicator in quantitative tenns of pollution strength.
There have been extensive investigations on appropriate methods to remove color from water for domestic use or wastewater from industrial processes. They include activated carbon, membrane sdsorption, cationic coagulation, polymer addition, ultrafiltration, biological, chemical oxidation and electrochemical methods. However these physical, chemical and biological color removal methods are often inefficient, or when they are efficient, they are unaffordable to most municipalities or factories as they are economically unsustainable.
Electrochemical or electro-coagulation method, in particular, is a well known for its effectiveness for removing color for most waters and wastewaters. However, over electrical potential within electrodes, normally causes extra voltage, which 'WBStes energy. Thus, electro-coagolation method for color removal can be applied only if there is a way to offset the high cost of power consumption through the recovery of high-value by-products such as in the case of metal plating. With this new method, we propose to substantially reduce power consumption during electro-coagolation color removal. This new method referred to hereafter as "ELCAS" is expected to cut power consumption by over 85%, thereby making electrochemical color removal method, not only highly efficient, but inexpensive and affordable. ELCAS is expected to enable most factories meet stringent effluent discharge standards.
There have been various methods used is an attempt to purify wastewater or raw water, which is colored.
EP016430 issued to Smolcoc, Vlsdislav discloses a process for clarifying colored wastewater using coagulation adsorption. This process does not address the cost implications of the power in electrolysis and the color removal.
EP0595178 issued to Bsumer and Horstick describes an electrolysis chamber for putifying wastewater efficiently with low conswnption of electrical cwrent. However, it does not address the issue of color effectively and even the cwrent consumption is still significant.
EP0597290 given to Bsumer and Horstick also, discloses a process in which the wastewater is purified by electrolytic coagulation to remove especially heavy metal impurities. In this invention, the significant improvement is in the keeping of a porous iron mass used in the treatment for a longer period.
There have been other extensive investigations on appropriate methods to remove color from water for domestic use or wastewater from industrial processes. These previous investigations have led to inventions that are almost economically WlSuitable.
Summary of the invention
The present invention relates to a method for treatment ofwaste'WB.ter from industry, especially, on raw water from rivers or related sources. This method may not require a major physical modification of a conventional wastewater treatment system. Some of the advantages of this method are the overall cost reduction in terms of time and finances. In this invention, wood ash is mixed with waste'WB.ter before the resulting solution is passed through an electrolysis process. There is a number of known electrolysis or electro-coagulation processes for the treatment of wastewater such as that disclosed in W09926887 in 1999, which cao be applied on the resulting mixture. In this invention, the ratio of the ash to Vr'BStewater is also crucial for efficiency in maximum color removal. Apart from the mtio, the detention time (holding time or retention time) in the compartment where electro-coagolation takes place is of great importance to ensure low power consumption. Thus a holding time of around one minute (or less) is recommended.
For other types of wastewaters higher deteotion times (higher than a minute) could prove more adequate to ensure maximum color removal.
When the color has beeo removed, the treated wastewater can be recycled back to the factory for re-use, with or without further treatment) depending on the quality of the process water required in a particular factory. In this sense, it also adds to the cost reduction and also reduced taping of the raw water from the natural systems. In effect, it causes fewer disturbances to the natural ecosystems (biological, chemical and physical).
During electro-coagulation, several electrodes plates can be used to achieve a certain surface area per unit volume ofVIBSte'WB.ter. This is the combined surface of the electrodes in relation to the volume of the wastewater to be treated. The electrodes themselves can be preferably "mild steel" for cost considemtion. Mild steel is a material that can be made readily available.
However, it should be noted that other conducting material can be used. It is also important to mention that because of the short detention time, there is eventual saving on the rate of deterioration of the electrode mass.
It should also be noted further here that power reduction using this method in comparison with other electro-coagulation color removal methods is more than 85%. There is over 80% biochemical oxygen demand (BOD) removal, and over 85% chemical oxygen demaod (COD) removal. There is no notable change in the pH in the treated waters. Further to these, there is increased tnmsparency of the treated wastewater, giving it a natural look. Over 95% turbidity reduction and over 99% reduction in total suspended solids (TSS) and total solids (TS) is achieved when using this invention. There is a significant reduction in concentration of contaminating metal ions. This, together with other factors, implies that there is tremendous reduction in the wastewater toxicity. It is also important to mention here that the odor of the
water is also reduced in the case of factories such as those of pulp and paper that use chemicals resulting in effluent being odorous. The ability of wastewater from pulp and psper mills to foam is considerably reduced. From all these beneficial effects, it becomes obvious that the resulting treated wastewater can be released back into natural flow unless it bas to be recycled back to the factory.
In short, with this new method called "ELCAS", the power consumption during electro-coagulation is substantially reduced. Therefore, ELCAS is expected to enable factories meet stringent effluent discharge standards.
Brief description of drawing
Fig I is a schematic diagram of ECLAS for electrochemical color removal method
Fig 2 is a schematic diagram of ELCAS for raw water treatment
Description with the help of drawings of preferred embodiment
Starting with Fig. I, wood ash Ll from collector tank I is let to flow through pipe P2 at the bottom of the tank to junction Jl. At the same time, wastewater WI in collector tank 2 is allowed to flow through the side pipe PI to junction Jl. At Jl, the wood ash Ll mixes with wastewater as they flow through the pipe B2 into compartment Cl of tank 3. It should be noted that wood ash/wastewater mtio should prefembly in close proximity of 0.278kg/m3. In compartment Cl in tank 3, wood ash is thoroughly mixed with wastewater in specific ratios. The overflow from Clgoes into compartment C2, through a provision Al on the connecting waH between Cl and C2. In C2, wood ash is allowed to settle and the supernatant allowed to flow into compartment C3. AI and A2 are walls opened at the top and bottom, and constructed in such a way that they stop 30 em above the bottom of Cl and C2 respectively. Their fimction is to reduce any turbulence created in Cl and C2, and ensure laminar flow into C2 and C3. In C3 the ntixture is allowed to settle further. From C3, the leachate then flows through pipe 19a into treatment tank 4 by gravity or any other means. The pipe 19a must be designed in such a way that the wastewater leachate is released at the bottom of tank 4, through orifices drilled on the pipe I9a. The exit velocity from pipe 19a should be high enough to ensure high turbulence and good mixing in tank 4. If good ntixing is not obtained, the overall electro-coagulation result will be affected. A ntixing pump can be used, but this will add to the treatment cost. In tank 4 a set of three iron electrodes (preferably ntild steel for cost effectiveness) lOa, lOb, !Ia, lib, 12a, 12b are used. The first lOa, lOb and third lla, lib electrodes are connected to an electrical power supply cathode and anode respectively. The electrodes are separated by non-conducting material 12a and 12b and the distance of separation can be kept at twenty (20) to thirty (30) centimeters. Several sets of electrodes can be used in parallel until a specific surface area is obtained; the preferable one being (0.0645 m2/m3 of wastewater). The distance of separation between
electrodes can be reduced as long as the specific surface area (0.0645 m /m ) is maintained. The preferred thickness of the ntild steel electrodes is 3.175 mm. The mass loss of electrodes is supposed to amount to only a maximum of0.086% per year. This means that a set ofntild steel electrodes can be used until the surface reduction is statistically significant.
Once a required amount of wastewater has flown into tank 4, the current is switched on. The wastewater is allowed in so that the detention time in tank 4 is kept at maximum one minute for minimum power consumption. During the treatment of wastewater in tank 4, the electrodes I Oa,
JOb, Jla, Jlb,12a, 12c, may foul. To avoid this fouling of electrodes washing can be done using 5% sulphuric acid. In this case, the assumption is that they are constructed in such a way that they can be removed for washing or a means for washing with acid is provided for in tank 4. The foam 20 formed on the surface of the wastewater in tank 4 is skimmed off by a sludge skimmer 18. Any sludge settling at the bottom 21 together with the foam 20 formed is passed through sludge draw of pipes 13 into the sludge -settling tank 6.
Therein tank 4 is provided a compartment 23 between the inner wall 17a and outer wall J7b. The supernatant 24 overflows a meshed wall provision 16 at the top of the inner wall17a into compartment 23. It then flows out through pipe 25 and it is collected in tank 5. In addition, the supernatant 22 from secondary sludge-settling tank 6 is allowed to flow through provision compartment 26 between the inner wall14a and outer wal!J4b of tank 6. It then goes into pipe 27 and finally into tank 5. Treated wastewater in tank 5 is either discharged into the river after further polishing (which may include anaerobic treatment for instance) or basically recycled back to the factory (mill).
Back to tank 3, the wood ash that settles out at the bottom is collected through pipes 28a, 28b, and 28c into 28d, which ends up in exhausted ash collector tank 8 for disposal. In tank 6, the sludge is allowed to settle after which it is collected from the bottom through pipe 29 which ends op in sludge collector tank 15 for further processing such as thickening and drying before ultimate disposal in a landfill.
For the treatment of raw water as shown in Fi.2, the process is the same except that, instead of tank 2 having wastewater wl, it bas raw water W2. This raw water undergoes a similar method of processing and treatment as that of wastewater up to the point where the treated water is in tank 5. From this point, the water is passed through pipe 30 into a filtering bed 31. After filtration through medium 34, it is piped through pipe 32 into tank 33 for recarbonation if necessary. This water is then allowed out through outlet 35 for disinfection before distribution.
A method of treatment of wastewater or water where the wastewater/water to be treated is first mixed with wood ash at a ratio of 0.278 kg of ash per m3 of wastewater/water. The resulting wood ash leachate is first allowed to settle to remove larger debtis before it is sul3jected to electro-coagulation to remove color. The detention time of leachate during electro-coagulation is kept at a maximum of one minute to ensure minimal power conswnption. Further to this, the ratio of electrode surface area to volume of water is kept close to 0.0645 m2/m3•
!.A method of total color removal from wastewater characterized by mixing the wastewater and wood asb at a specific ratio after which the resulting leachate is subjected to electro-coagulation whose electrodes total surface area is specific in relation to the volwne of wastewater. The detention time during electro-coagulation in this case is kept at a minimwn.
2. A method of color removal from wastewater as in claim l characterized such that the mass to wastewater volume ratio is 0.278 kglm3•
3. A method of color removal from wastewater as in claim I characterized such that the ratio of total of elec1rodes surface area to volume of the ash leachate is 0.0645 m2/m3•
4. A method of color removal from wastewater as in claim l, characterized such that the holding time in the electro-coagulation chamber or tank is kept at less than one minute.
5. A method of wastewater color removal as in claims 1 and 4 characterized by low mass loss
(maximum of 0.086% per year).
6. A method of wastewater color removal as in claims l-4 characterized by reduction in odor.
7. A method of wastewater color removal as in claims l-4 characterized by reduction in concentration of contaminating metal ions.
8. A method of wastewater color removal as in claims l-4 characterized by reduction in TSS and TS by over 99%.
9. A method of wastewater color removal as in claims 1-4 characterized by reduction in turbidity byover95%.
10. A method of color removal from wastewater as in claims l-4 characterized by BOD removal ofover80%.
11. A method of color removal from wastewater as in claims l-4 characterized by COD removal ofover85%.
12. A method of color removal from wastewater as in claims l-4 characterized by low electric power consumption (at least 85% less than conventional electro-coagulation method alone).
13. A method of total color removal from raw water characterized by mixing the raw water and
ash in specific ratio, after which the resulting leachate is passed through an electro-coagulation chamber whose electrode total surface area is specific in relation to the volwne of \Vater. The detention time during electro-coagulation is in this case kept to a ntinimum.
14. A method of color removal in water as in claim 13 characterized by the ash mass to raw water volume ratio is 0.278 kglm3•
15. A method of color removal from raw water as in claim 13 characterized such that the total electrodes area to volume of the asb leachate is 0.0645 m2/m3•
16. A method of color removal from raw water as in claim 13, characterized such that the holding time in the electro-coagulation chamber or tank is kept at less than one minute.
17. A method of color removal from raw water as in claim 13-16 characterized by low electrode mass loss (maximum of0.086% per year).
18. A method of raw water color removal as in claims 13~16 characterized by reduction in odor.
19. A method of mw water color removal as in claims 13~16 characterized by reduction in concentration of contaminating metal ions.
20. A method of raw water color removal as in claims 13-16 characterized by reduction in TSS and TS by over 99%.
21. A method of raw water color removal as in claims 13-16 characterized by reduction in turbidity by over 95%.
22. A method of color removal from raw water as in claims 13-16 characterized by low electric power consumption (at least 85% less than conventional electro-coagulation method alone).
(11) Patent Number: KE 400