The following are the adverse impacts of building and operating sewage treatment plants. For Victoria they outweigh the scant reasons for building them.
The fuel use and exhaust generated by spending an amount equal to the construction of 12,000 / $100,000 houses.
The same in perpetuity for the daily transportation of sludge.
Injury risks in a billion dollars worth of civil engineering; statistically over fifty people are liable to suffer permanent impairment (such human losses are tolerated for civil engineering work that is needed but is inexcusable, in my view, where it is not).
The risk of injury in plant operation (compared to most industrial operations, the open tanks and weather exposure put them at the high end of risk): see www.ilo.org/public/english/protection/safework/cis/products/hdo/htm/oper_wastewtr.htm for 28 possible hazards).
Risks from pathogenic aerosols. These were not thought to affect operators, based on their general health, but recent research is troubling. An abstract from a paper at email@example.com reads
investigations suggest that gastrointestinal tract symptoms are more common among employees at sewage treatment plants than among controlsRespiratory symptoms, fatigue, and headache have also been reported in several investigations. (Nothing made me ponder longer about the SETAC report than their reference to pathogens sometimes being able to reach the sea surface but making no mention of pathogens at treatment plants. In the one case diluted waste rises 200 feet through bitterly cold salt water a mile offshore. In the other air pours up 20 feet through untreated sewage with operators moving round and houses not far away).
The energy used in plant operation. Air compressors will be running 24 hours a day 365 days a year and it is doubtful if the plants will be big enough to allow generation of electricity from the plant gases.
Plant failure. Rare but already other CRD plants have failed. When they do they do not purify the sewage, and may stink. Operation depends on electrical and mechanical equipment and human beings!
The dubious impact of taking minute quantities of toxic metals in a form that does no harm and concentrating them into a sludge to put on land.
The loss of land to be dedicated to sludge disposal.
The damage to land uses. No-one wants a sewage plant near them nor the passage of trucks, people and equipment that plant operation entails.
The damage done to the local economy by diverting so much purchasing power from the public to taxes, far outweighing the dubious benefit from more tourists.
In total these adverse impacts are substantial but pale compared with the loss of environmental benefits the money could bring spent in other ways.