DEMM Engineering & Manufacturing - - EDITORIAL -

OP­ER­AT­ING WASTE­WATER treat­ment plants in flood- prone and sandy areas through­out New Zea­land and Aus­tralia is fraught with haz­ard. Over­flows and clog­ging re­sult­ing from storms can not only re­sult in smelly, un­healthy and dam­ag­ing dis­charges into en­vi­ron­men­tally sen­si­tive wa­ter­ways, but also pose OH&S haz­ards to those charged with the dirty and heavy work of clean- ups.

One or­gan­i­sa­tion that has over­come the prob­lem in a long-term and cost- ef­fi­cient man­ner is the Rich­mond Val­ley Coun­cil, which is now reap­ing the div­i­dends of in­stalling fine screen­ing and waste extractor tech­nolo­gies at its Casino Sewage Treat­ment Plant.

The fine grit ex­trac­tion tech­nol­ogy sup­plied by CST Waste­water So­lu­tions for this retro­fit is suit­able for both lo­cal au­thor­ity and in­dus­trial ap­pli­ca­tions, such as food and bev­er­age, man­u­fac­tur­ing and pro­cess­ing, min­ing, en­ergy and re­sources camps where its low main­te­nance, high hy­giene qual­i­ties are ap­pre­ci­ated. It is also ap­pli­ca­ble to agribusi­ness and in­stal­la­tions where low main­te­nance and high ef­fi­ciency is a pri­or­ity for users who don’t need to have spe­cial­ist staff con­stantly avail­able.

In the Casino ap­pli­ca­tion, the new screen­ing and grit re­moval tech­nolo­gies have proved them­selves in ser­vice over more than a year in the North­ern Rivers Re­gion, where rain­fall can vary from about 600-2900mm a year, with in­di­vid­ual falls ex­ceed­ing 150mm.

The Casino retro­fit project re­placed the pre­vi­ous coarse raked screen de­sign, which not only al­lowed more solids to pass through to foul pro­cess­ing down­stream, but also had to be man­u­ally and la­bo­ri­ously raked out when they clogged dur­ing high-flow events.

The new screen­ing retro­fit – com­bined with grit re­moval and clean bag­ging pro­cesses – cap­tures more solids to re­duce po­ten­tial block­ages in tanks and down­stream equip­ment, while re­duc­ing odours by seal­ing the in­let works and by the in­stal­la­tion of new odour con­trol units. The project’s high- ef­fi­ciency fine screen­ing SF tech­nol­ogy (Screen Extractor For Chan­nel In­stal­la­tion com­bined with a CST Screw Com­pactor) is en­gi­neered to de­liver low-main­te­nance per­for­mance with re­duced WHS haz­ards for mu­nic­i­pal and in­dus­trial waste­water op­er­a­tors.

The SF al­lows for a much finer level of screen­ing – 5mm com­pared with typ­i­cal old sys­tems at 60mm or more – which has led to a sig­nif­i­cant re­duc­tion in solids in the tanks, while pro­duc­ing more ef­fi­cient treat­ment with less main­te­nance.

Spec­i­fied to han­dle flows of up to 500 litres a sec­ond, the Casino in­stal­la­tion has coped flaw­lessly with ev­ery­thing na­ture had to throw at it in its first year of op­er­a­tion, in­clud­ing some of the worst floods in the dis­trict for years.

“It just keeps on turn­ing over, tak­ing out the waste that could block the sys­tem’s down­stream pro­cesses and cause un­wanted dis­charges and main­te­nance,” says Casino WWTP Se­nior Op­er­a­tor Robert Sabol.

“Now we have no over­flows. We can con­fi­dently leave it to op­er­ate overnight, know­ing that it just keeps on work­ing. We’re not wor­ried about com­ing back to find it has over­flowed,” he says.

Com­pacted and de­wa­tered waste ex­tracted from the sys­tem is au­to­mat­i­cally chan­nelled into wait­ing bag­ging con­tain­ers, where it is neatly col­lected with­out the need for di­rect han­dling of waste.

Nor do op­er­a­tions staff have to get into the screen­ing sys­tem with rakes and levers to clear block­ages, which was a time- con­sum­ing and messy busi­ness with old coarse screen­ing.

“Ser­vic­ing of this sys­tem in­volves next to noth­ing com­pared with the old way. It is so easy and ef­fi­cient. It can’t get any eas­ier, whereas the old coarse screen would just clog up and block.” Sus­tain­abil­ity of the new sys­tem is fur­ther en­hanced by the en­ergy sav­ings it pro­duces, typ­i­cally .8kw on a 24- hour cy­cle.

The Casino retro­fit also in­volved the in­stal­la­tion of an SDS 20 com­pactor with two in­lets – one for each screen – to de­wa­ter screen­ings to 25-30 per­cent dry solids. Each screen has an en­hanced de­sign ca­pac­ity of 250L/s flow, pro­vid­ing a to­tal ca­pac­ity of 500L/s.

The orig­i­nal in­let works at Casino STP were de­signed with a coarse man­ual raked bar screen sys­tem. The func­tional com­po­nents of the treat­ment process down­stream of the bar screen re­ceive a high amount of de­bris, which for­merly im­pacted the ef­fi­ciency of the treat­ment process. The orig­i­nal in­let area also re­ceived a high amount of odor­ous gases, which pre­vi­ously con­tributed sig­nif­i­cantly to odours em­a­nat­ing from the treat­ment plant. In ad­di­tion to min­imis­ing th­ese is­sues, the up­grade project in­volved fit­ting new tech­nol­ogy into an ex­ist­ing lay­out, in­clud­ing tai­lor­ing the screens to fit into the ex­ist­ing formed chan­nel.

CST Waste­water So­lu­tions’ ro­bust and proven units are con­structed from AISI 304 or 316 stain­less steel with­out the need for hanger, in­ter­me­di­ate or bot­tom bear­ings. Fea­tur­ing a space- ef­fi­cient de­sign suited to small sewage plants, the stan­dard unit can han­dle up to 1000m3 an hour with cus­tom en­gi­neer­ing also avail­able for par­tic­u­lar in­stal­la­tions. A ver­ti­cal ver­sion is also avail­able to eas­ily retro­fit into ex­ist­ing pump sta­tions, and, with depths up to 8m, the screen al­lows re­moval of ma­te­rial be­fore pump­ing.

The ver­sa­tile SF Screen Extractor can be in­stalled in a chan­nel or sup­plied with self- sup­port­ing tank, com­plete with in­let and out­let flange and op­tional by­pass scree.



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