The upgrade will make the current process largely redundant meaning the accumulated sludge in both ponds at the Airport Rd site must be removed, have the water extracted before it is dried and dumped.
Mark Hughes, council's infrastructure manager, told the Chronicle that accelerating the sludge removal means that part of the operation should be finished in March.
Mr Hughes said the good news is that the odour from the plant is not as bad as this time last year.
"We expect the lower level of odour to continue until Easter when the pond will be empty and odours a thing of the past.
"We haven't received any unexpected loads from our wet industries which has certainly helped and for that we thank them and ask that they continue this good practice," he said.
Meanwhile, a shortlist of five companies has been selected for council to evaluate as the preferred contactor for the upgrade.
Council undertook an open expression of interest process in November and December last year and from that 11 companies from New Zealand and overseas registered their interest in tendering for the construction of the new plant.
"These companies were evaluated on qualitative criteria, including past experience and capability, and six were selected to participate in the process," Mr Hughes said.
"One company has subsequently withdrawn from the process due to their other current commitments and available resources. The five remaining companies are all NZ-based."
Tenders close on February 18 and the evaluation and clarification process is expected to take another two to three weeks before the council can appoint the successful contractor.
Council and the contractor will then work together to produce the "for construction" documentation.
"This will enable council to take full advantage of the contractor's experience and incorporate any alternative construction methods."
Mr Hughes said that documentation was expected to be issued by Easter, when the contractor will be on site.
