As wa­ter scarci­ty con­tin­ues to be one of the largest chal­lenges fac­ing so­ci­eties to­day, de­sali­na­tion re­mains one of the more re­li­able meth­ods of pro­vid­ing safe and clean wa­ter. The glob­al de­sali­na­tion sec­tors con­tin­ue to grow rapid­ly and the im­pe­tus for re­duc­ing the ad­verse en­vi­ron­men­tal im­pacts of brine (waste­water) dis­charge grows con­cur­rent­ly.

One of the ma­jor en­vi­ron­men­tal re­lat­ed is­sues with sea­wa­ter de­sali­na­tion is the gen­er­a­tion of brine (as­so­ci­at­ed waste­water high in salt con­cen­tra­tions) and brine dis­charge. For sev­er­al de­sali­na­tion plants across the globe, the most prac­ti­cal and eco­nom­i­cal brine dis­pos­al method is dis­charg­ing it in­to the sea at the wa­ter treat­ment plant’s out­fall. This re­sults in the largest en­vi­ron­men­tal im­pact of most de­sali­na­tion plants on the en­vi­ron­ment oc­cur­ring at the out­fall to the re­spec­tive seas/ocean. Fur­ther­more, there are sev­er­al harm­ful en­vi­ron­men­tal ef­fects (wa­ter tem­per­a­ture, salin­i­ty, dis­solved oxy­gen con­tent, pH and al­ka­lin­i­ty flux­es) caused by this di­rect dis­charge of brine. This dis­charged brine (con­cen­trate waste­water) has many phys­i­cal, chem­i­cal and bi­o­log­i­cal prop­er­ties, which can bad­ly af­fect any en­vi­ron­ment if not treat­ed, re­cy­cled or dis­posed of sus­tain­ably. Brine so­lu­tions can some­times con­sist of high­ly con­cen­trat­ed salts and any un­re­act­ed pre­treat­ment chem­i­cals used in the wa­ter treat­ment process. Brine can al­so bring with it some heavy met­als re­sult­ing from cor­ro­sion of pipelines and walls of ma­te­ri­als with­in the treat­ment works.

Al­though mod­ern brine out­fall de­signs have sig­nif­i­cant­ly lim­it­ed such en­vi­ron­men­tal im­pacts, they are cost­ly. Re­cov­er­ing valu­able com­po­nents and chem­i­cal de­riv­a­tives from brine has the po­ten­tial to re­solve both en­vi­ron­men­tal and eco­nom­ic con­cerns. There is def­i­nite­ly an en­vi­ron­men­tal prob­lem with brine man­age­ment, but there are so­lu­tions for deal­ing with brine and waste­water gen­er­at­ed from the de­sali­na­tion pro­duc­tion process­es. One such pro­pos­al is the on-site gen­er­a­tion of sodi­um hypochlo­rite (NaO­Cl), on-site at the wa­ter treat­ment (de­sali­na­tion) Plant.

On-Site Gen­er­a­tion of Sodi­um Hypochlo­rite from de­sali­na­tion fa­cil­i­ties has been in com­mer­cial use for over 45 years. This tech­nol­o­gy sheds some light on the busi­ness op­por­tu­ni­ties as­so­ci­at­ed with brine waste streams by us­ing the brine so­lu­tion for on-site gen­er­a­tion of sodi­um hypochlo­rite. How­ev­er, the tech­nol­o­gy has not been as wide­ly utilised in wa­ter treat­ment plants due to the op­er­at­ing costs com­pared to that of bulk chlo­rine prod­ucts.

Sodi­um hypochlo­rite is a use­ful and valu­able wa­ter dis­in­fec­tion prod­uct. It is used as a bleach­ing and dis­in­fect­ing agent and is com­mon­ly found in house­hold bleach prod­ucts. It is wide­ly used as an ac­tive com­pound in the dis­in­fec­tion process. Sodi­um hypochlo­rite can be used for chlo­ri­na­tion to pre­vent bac­te­r­i­al growth with­in the de­sali­na­tion fa­cil­i­ty. The sub­sti­tu­tion of chlo­rine with on-site pro­duced sodi­um hypochlo­rite can im­prove the de­sali­na­tion process­es en­vi­ron­men­tal­ly. There is a dual ben­e­fit of on-site gen­er­a­tion of sodi­um hypochlo­rite re­duc­ing the vol­umes as well as the con­cen­tra­tions of brine gen­er­at­ed. Be­cause this tech­nol­o­gy can elim­i­nate de­pen­den­cy up­on out­side sup­pli­ers and the high costs of pur­chased im­port­ed com­mer­cial prod­ucts, it can be ap­plied in a broad spec­trum of in­dus­tri­al fa­cil­i­ties re­quir­ing bi­o­log­i­cal growth con­trol across var­i­ous wa­ter sys­tems. This pro­posed tech­nol­o­gy of on-site gen­er­a­tion of sodi­um hypochlo­rite so­lu­tions from sea­wa­ter is to eco­nom­i­cal­ly and safe­ly pro­duce a pow­er­ful bio­cide and dis­in­fect­ing agent for use in in­dus­tri­al plants. There­fore, the process will not on­ly gen­er­ate the sodi­um hypochlo­rite, but can al­so pro­tect the en­vi­ron­ment from un­sus­tain­able brine dis­charge.

There are sev­er­al large wa­ter treat­ment plants and com­mer­cial swim­ming pools world­wide util­is­ing on-site sodi­um hypochlo­rite gen­er­a­tion sys­tems from de­sali­na­tion wa­ter treat­ment plants. In ad­di­tion, Oc­cu­pa­tion­al Health, Safe­ty and En­vi­ron­men­tal is­sues have caused wa­ter util­i­ties and en­gi­neers to spec­i­fy the tech­nol­o­gy in place of chlo­rine gas and com­mer­cial grade sodi­um hypochlo­rite. Fur­ther­more, gen­er­at­ing sodi­um hypochlo­rite on-site can be a vi­able, cost-ef­fec­tive and safe al­ter­na­tives to com­mer­cial grade liq­uid or gaseous chlo­rine used in dis­in­fec­tion. Tak­ing safe­ty is­sues in­to ac­count, it is still a vi­able al­ter­na­tive for wa­ter util­i­ties.

Fu­ture re­search and pi­lot-scale demon­stra­tions need to bring this tech­nol­o­gy to com­mer­cial fea­si­bil­i­ty in the Caribbean.

Head of Civ­il & En­vi­ron­men­tal En­gi­neer­ing

Cen­tre for Wa­ter, Com­mu­ni­ties and Re­silience (CW­CR)

Uni­ver­si­ty of the West of Eng­land (UWE Bris­tol)

Bris­tol, UK

Email: Ki­ran.To­ta-Ma­haraj@uwe.ac.uk

Face­book: https://www.face­book.com/UWE­Civi­lan­dEn­vi­ron­men­tal­Engi­neer­ing/