Carterton District Council will trial a greener approach when it comes to disposing sludge from its wastewater ponds.
At a Policy and Projects committee meeting on Wednesday, councillors endorsed a trial to compost the waste, which could stand to make the council money, if successful.
Council infrastructure services manager Johannes Ferreira said disposing of wastewater sludge was a challenge facing many councils across New Zealand.
Wastewater treatment plants used stabilisation ponds, or oxidation ponds, to treat wastewater.
Over time, bio-solids build up in the bottom of these ponds as sludge – a byproduct of the treatment process.
The sludge must be periodically removed, or it reduced the treatment ponds efficacy.
“There are a lot of councils with a stockpile of sludge on their properties that they can’t dispose of or are disposing of at an extreme cost,” Ferreira said.
Typically, councils removed the sludge, dried it, and sent it to landfill or stored it.
Ferreira said Carterton District Council had worked with professional service providers Vitruvius and Composting NZ to develop a solution for the de-sludging, treatment, and disposal of the final product.
At a high level, the solution included de-watering the sludge, removing it from the oxidation pond, composting biosolids, compliance testing, and disposal of compliant compost.
“Apart from the obvious advantage that we won’t have a stockpile of sludge in our property, there’s an added benefit in the future that we could be positioning ourselves to accept sludge from other councils that are currently dealing with the problem and don’t yet have the solution,” Ferreira said.
A report to council said AA-grade compost could be applied to agricultural land as fertiliser.
“Because of the council’s earlier strategic decisions to acquire Daleton and Matarawa Farm, there is now a new opportunity to accept sludge from other councils in the future,” the report said.
“If successful, this initiative could offer council an additional source of revenue.”
The current approved budget for de-sludging meant only 30-50% of the current sludge would be dealt with.
Removing this amount, up to 1000 tonnes, would still significantly improve the health and effectiveness of the pond.
Another option councillors considered was to progress with the de-sludging only, but this would mean about 2000 tonnes of sludge would be stockpiled on site without a detailed disposal plan.
Mayor Ron Mark said he liked the opportunity for revenue generation, going forward.
“It’s innovative and taking a cautious step forward.”
The trial aligned with goals in the council’s Long-Term Plan, one of which was to investigate a holistic and sustainable solution for biosolids management.
Neighbouring South Wairarapa District Council was desludging its wastewater ponds in Martinborough and Greytown after new connections were put on hold in each town due to capacity issues.
It was using a method which involved pumping or vacuuming sludge into sediment filter bags, or geobags.
The geobags allowed water to flow out through the porous fabric of the bags while filtering and retaining the solids.
The remnants would later need to be disposed of.
The desludging work at Martinborough would improve treatment plant efficiency, but was not a solution that would address Martinborough’s capacity constraints for new connections.
LDR is local body journalism co-funded by RNZ and NZ On Air
