Patent Application: US-201314373051-A

Abstract:
method of producing biocides from an aqueous flow of process water , said method comprising the step of subjecting a water flow containing ions which give rise to conductivity through an electrolysis cell in order to generate chemicals with biocidal performance . the method can be used for treating fresh and waste water systems , such as water streams of cooling systems , fermentation , mining and biorefining , for example papermaking process waters . it can be used for reducing halogen concentration .

Description:
as discussed above , electrochemical generation of oxidants has been studied to find new solutions to control microbial contamination in process waters . the present approach has been used for generating the biocides directly from the process without any chemical additions . in the present context , the technology has been applied into the papermaking process but it is applicable to any aqueous process requiring microbial control . as the below examples comprising laboratory electrolysis trials indicate direct electrolysis of process waters is an efficient new concept to control microbial contamination at paper mills . electrolysis considerably reduces the need of halogen containing biocides , thus lessening risk of corrosion . instead of increasing halogen concentration like with the conventional stabilized halogen biocide systems , the electrolysis concept is capable of decreasing the concentration of halogens in the process waters . at the same time the conductivity of the process waters decreased indicating process purifying effect in addition to biocidal effects . the trials with samples from paper machines indicate that the new concept can be applied into several process stages . in addition to killing effect the electrolysis was able to produce excess amount of active halogens which turned contaminated process water into biocide with substantial biocidal effectiveness . direct electrolysis of process waters enables on - site biocide production which eliminates all transportation costs , risk associated with storage of hazardous chemicals and biocide lost due to degradation . thus , biocidal effects together with reduction in amount of halogen containing oxidants and reduction in process conductivity make this concept economically attractive and environmentally positive . in the method of producing biocides from an aqueous flow of process water , a water flow containing ions , such as halogens , which give rise to conductivity are conducted through an electrolysis cell in order to generate chemicals with biocidal performance . the halogens are typically comprised of chlorine or bromine compounds . the method comprises , in a preferred embodiment , simultaneously decreasing the conductivity level of the process water by decreasing the halogen concentration . in particular , the process water flow is subjected to direct electrolysis . typically , the process water flow is subjected to electrolysis in order to reduce conductivity of the water with at least 5 %, in particular at least 10 % and preferably with at least 15 to 85 %, e . g . with at least 20 %. in one embodiment , the water is subjected to electrolysis in an electrochemical cell . generally , in the present technology , the water is subjected to electrolysis using a current in the range of 0 . 1 to 1000 a , for example about 1 to 150 a , for example 1 to 100 a . the voltage of the electrolysis varies broadly , from for example about 0 . 1 to 1000 v , for example the voltage is about 1 to 250 v . the electrolysis can be carried out for clear water streams . the method can also be carried out for process waters having a consistency of about 0 . 1 to 20 % by mass . process water and furnishes were taken from several parts of a paper machine at a finnish fine paper mill ( table 1 ). total bacterial count at sampling is shown in fig1 . the electrochemical cell ec - electro mp ( electrocell , denmark ) was employed for electrolysis . this is a modular multipurpose cell intended for process evaluations and experimental tests on laboratory scale . the structure of this filter - press type cell is shown in fig2 . the projected electrode area was 200 cm2 , and the distance between cathode and anode was 3 mm . titanium was employed as cathode , while dsa ( dimensionally stable anode ) as anode . dsa is iridium and ruthenium oxide coated titanium . according to the distributor , the ratio of iridium oxide and ruthenium oxide is 70 / 30 . it has high oxygen over - potential and is corrosion - resistant . as a power source , switch - kraft type sk 075b ( kraftelektronik ab , sweden ) was used in the electrolysis . the maximum current and voltage of this rectifier are 50 a and 15v , respectively . all the electrolysis experiments were in the controlled - current mode and anode was continuously cooled down by water circulation system at 5 ° c . experimental setup is shown in fig3 . superfiltrate sample was pumped into the cell where electrolysis was taking place . the temperature of the product was monitored after the cell , and the mixture of chlorine and oxygen gases was diluted with air and discharged . ph , orp ( oxidation reduction potential ) and conductivity were also measured . all of this data was recorded in a computer . treated white water samples were taken aseptically from test trials and transported in sterile plastic vials to laboratory . samples were cultured within three hours . logarithmic dilution series were prepared using sterile ringer &# 39 ; s solution . culturing was performed by pipetting and spreading 1 ml diluted sample on aerobic count petrifilm ( ac ). incubation took place in 30 ° c . for 3 days . red colonies were counted from ac petrifilms containing 3 to 300 colonies . the biomass of samples were studied using atp biomass kit hs ( biothema , sweden ). tests were performed according to manufacturer &# 39 ; s instructions : 0 . 05 ml undiluted sample was pipetted in cuvette with reagents , light output was measured and atp - standard was added and light output was measured again . free available chlorine in the electrolyzed superfiltrate was measured by photometer , dulcotest dt1 ( prominent , germany ). ph and conductivity were measured using ysi 556 mps ( ysi incorporated , usa ) multi - parameter probe . ysi professinoal plus ( ysi incorporated , usa ) multi - parameter probe was used to analyse the chloride content . total bacterial count in the electrolyzed superfiltrate water was given in fig4 . bacteria were killed in electrolysis cell . the number depends on the current and flow rate , i . e . higher current or lower flow rate was more effective to reduce the bacteria . for this filtrate water , & gt ; 4 a current with & lt ; 80 ml / min flow rate turned out to be enough to kill almost all bacteria . in practice this indicates , that the approach is more than capable of treating the process samples to ensure microbiologically clean process . in fact , it is probable that in case of high current and / or low flow rate the electrolysis generates excess amount of biocidal compounds . fig4 shows the effects of current and flow rate on total bacterial count in super sample . flow rate was fixed at 80 ml / min in the current trials ( left ), while current levels were fixed at 4 a and 7 a in the flow rate trial ( right ). as shown in fig1 , total bacterial count of superfiltrate was not so high compared with white water , headbox furnish or broke . therefore one can expect that superfiltrate processed with higher current should still retain biocidability . this was simply checked by mixing the electrolyzed superfiltrate ( at 7 a , 80 ml / min ) with the original superfiltrate . as shown in fig5 a , it behaved as biocide as expected . 17 % dosage was enough to kill 99 % of bacteria in the original superfiltrate . it was also mixed with other samples to find its biocidability too ( fig5 b , 5 c , 5 d ). here higher dosage ( 33 %) was required to kill 99 % bacteria , simply due to larger number of bacteria in those samples . also higher fiber consistency of the other samples may have affected the reduced biocide performance . this is well known feature of some oxidants , which are not highly selective in killing but are consumed by all organic material in the sample . fig5 shows biocidability of electrolyzed superfiltrate against ( a ) original superfiltrate , ( b ) white water , ( c ) headbox furnish and ( d ) broke . total bacterial count was plotted against different dosage levels . in addition to superfiltrate , white water and headbox furnish were also applied for electrolyses . direct electrolysis was difficult due to their containing solids , thus we simply took the supernatant fraction after sedimentation and applied them for the electrolysis . the processed fractions were then returned back to mix with the original samples at different dosage levels . supernatant volume was 75 % for white water and 35 % for headbox , which limited the dosage level . as shown in the fig6 , both turned out to function as biocide as well as superfiltrate . as expected , the result of white water supernatant fraction ( fig6 a ) was similar to that of superfiltrate ( fig5 b ). free available chlorine in the electrolyzed superfiltrate was measured by photometer , dulcotest dti ( prominent ). measurements were repeated periodically to see the time dependence . as shown in fig7 , it decayed with time . almost all free chlorine disappeared within 3 hours . the biocidability was also decayed accordingly with time ( fig8 ). mixing right after the electrolysis was the most effective . however , fair effects remained for rather long time . generally ph increased with electrolyses . due to the complex composition of the sample , an unambiguous reason to this cannot be given . most likely the ph increase is due to formation of alkaline compounds such as naoh and h2o2 . one example is shown in fig9 for superfiltrate , i . e . from ph8 ( before ) to ph9 ( after ). here one may suspect that the biocidability derives simply from increasing ph . thus we carried out the verification trials with controlled ph . proper amount of hydrochloric acid ( hcl ) was added before the electrolysis to compensate in advance . then the results still showed biocidability in sufficient level ( fig1 a ). the impact as biocide was somewhat milder than the case without ph control ( fig5 a ). this could be explained by ph , of course . however , one can also speculate its reason as the reduction of total chlorine amount due to hcl ( causing c12 generation ). on the other hand , hypochloric acid is known to be the most effective biocidal compound in hypochlorite solution and its concentration is known to increase along decreasing ph . thus , due to these cross - effects , the effect of ph can be considered as rather insignificant for the biocide performance . for chemical stability of papermaking ph stability is known to be highly important [ 12 , 13 ]. therefore ph control of electrolysis flow according to process ph is recommended . in papermaking free anions and cations have significant roles . the functioning of most of the wet end chemicals is based , at least partly , on charge ( e . g . retention aids , fixatives , starch ). charge and conductivity are coupled , and thus any changes in conductivity may cause problems . naturally , electrolysis gave significant influence on conductivity . one example is shown in fig1 for superfiltrate , i . e . from 1 . 13 ms / cm ( before ) to 0 . 88 ms / cm ( after ). drop of more than 20 % in conductivity is significant . current state - of - the - art commercial oxidative biocide systems are mostly based on hypochlorite chemistry . for instance all hydantoin and ammoniumbromine technologies utilize sodium hypochlorite as a halogen source . commercial hypochlorite generation generates equal amount of salt ( c12 ( g )+ 2naoh naocl + nacl + h2o ). this salt amount in hypochlorite solution also further increases when hypochlorite decomposes . this means that in practice approximately ⅔ of the hypochlorite is actually sodium chloride ( salt ). this salt addition has several disadvantages : conductivity increase affect chemical interactions of particles in the process causing problems with retention , flocculation etc . unnecessarily added chloride increases risk of corrosion . any halogen addition increases the aox ( adsobable organic halogen ) load to waste waters . the electrolysis approach eliminates all these disadvantages . no salt is added actually the salt amount is reduced as shown in fig1 . this approach actually also enables addition of biocides without detrimental effects . thus we carried out the trials with compensating such conductivity drops by salt addition . here three salts were compared , i . e . sodium chloride ( nacl ), sodium bicarbonate ( nahco3 ) and sodium carbonate ( na2co3 ). electrolyzed superfiltrate was applied to white water as biocide . results are shown in fig1 - 14 . among the three , nacl was the most effective . in terms of energy consumption , nacl was also effective , i . e . voltage reduction by 1v ( 8 . 7v 7 . 7v at 7a ). on the other hand , nahco3 and na2co3 influenced little on the energy consumption . extensive addition cases are compared in fig . 15 for nacl and na2co3 . the voltage decreased linearly with conductivity increase in both cases . the addition of salt to the process might lead to increased agglomeration or to problems with retention [ 14 ]. changes in conductivity must be taken into account when selecting the chemicals for optimal process . biocide treatment of all loop waters to disc filter of a typical paper machine with production 300 . 000 t / a , and degree of closure 7 . 2 m 3 / t : in production , cell the electrode area is 16 m2 [ 15 ]. based on this study the capacity of such cell is to produce approximately 0 . 5 m3 / min purified , microbiologically clean process water . the production of the pm is approximately 0 . 5 t of paper per minute . process water flow to disc filter is thus approximately 19 m3 / min . therefore the electrolysis is able to treat 2 - 3 % of the process water flow to disc filter . for a typical biocide program this amount should be 5 - 10 %. as the above examples show , the positive features of the electrolysis technology for the process are obvious : increased process stability , together with the compensation of the disadvantages ( due to process closure and accumulation of dissolved and colloidal material ). at the same time , however , the decreased amount of halogens in the process has also positive impacts on corrosion risks and waste water problems . the other positive factors are mostly related to logistics and costs . the present novel technology does not require any transportation or production of hazardous materials . no biocides need to be transported to the production units . actually the present technology does not require any transportation at all . also the raw material for the on - site biocide production is extracted from the process . in case the biocide generation is boosted by the salt addition , only shipping of salt is required . otherwise only electricity is needed . also storage needs are minimal since the production can be performed according to the need . this is also recommended due to degradation of active compounds . 1 . kolari , m . 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