Anne Lee

Increasing storage, without increasing storage by the usual means at least, is proving to be one of the drawcards of Ravensdown’s ClearTech effluent technology.

The ability of the system to clarify much of the liquid portion of effluent coming from the farm dairy each day, allowing that water to be used in yard washdown means the amount of treated effluent heading for the storage pond can be cut to about a third of the original volume.

And it’s not just farmers who are seeing that benefit with trucking companies that also deal with effluent from truck washdowns installing the system.

Frews Transport general manager Chaz Frew says washing down truck and trailer units uses a lot of water and also creates effluent that needs to be dealt with.

His company has installed a system at its Darfield site and has immediately seen a dramatic drop in the amount of water needed from the town supply as the system allows them to keep recycling what’s coming off the washdown process.

The increase in the number of cattle transported as dairying has grown in the region has changed the nature of the what was left behind in the trucks and over the years they’d climbed to using three times more than their original consented water allocation.

For Canterbury dairy farmer Tom Mason the ability to reduce the volume of effluent produced each day at the family’s 550-cow Greenpark Dairies was a big plus despite the farm already having sufficient storage based on its consent.

“We wanted a bit more comfort through the shoulders of the season so we’re just never in the situation that we’re worrying about storing effluent.”

The farm’s pretty low lying and when the lake (Te Waihora/Lake Ellesmere) is high the water table comes up too so soil moisture, while good for grass growth, can’t take any additional inputs from irrigated effluent at those times.

The farm is an amalgamation of a couple of properties and until the last decade the land around the farm dairy had been a town milk supply farm since 1937.

“You can just about see every growth pain since it started its life as four-bail walk-through,” Tom quips as he talks about the development both before and after they bought that land and another adjoining block five years ago.

The concreted saucer and 267,000-litre Kliptank were installed by the previous owners and while it meets consent requirements Tom wanted to future-proof the farm and have peace of mind that best practice could be achieved every day of every season regardless of weather and soil conditions.

“If we can cut our effluent volume by two thirds that’s going to be significant for us,” he says.

It adds to a number of other shifts they’ve made to lighten the farm’s environmental footprint.

When they took over, they cut the stocking rate and switched to lighter, smaller Jerseys.

They moved to once-a-day milking through the spring as another tool to lighten any impact and reduce the volume of effluent coming through the system.

Those changes and a move to where virtually no supplement is bought-in means the farm system has slashed its Overseer nitrogen loss number by more than 40% compared with the farm’s losses during Canterbury’s regional plan baseline period 2009-2013.

Phosphorus and Eschericia coli (E. coli) are two other considerations for the area given the proximity to the lake and the historical drain systems that crisscross the district.

That’s where the other major benefits of ClearTech were significant bonuses.

“The numbers on P and E. coli reductions are pretty impressive and anything we do in that way has to be good.”

Drains that run through the farm all head towards the new

Te Ahuriri wetland on the Halswell River which is set to act as a natural filter.

Tom says the clarified water captured by the ClearTech system is sent to a 30,000-litre tank and has been plumbed through the backing gate yard wash system and to a handheld hose for the yard.

The cost of that plumbing, any additional pumps, electrical work, the water tank and remedial work to the site where the ClearTech system sits is in addition to the system itself and Tom says it wasn’t an insignificant amount in their case.

ClearTech product manager Carl Ahlfield says the system price is $88,000 which covers the cost of the ClearTech tanks, the control unit which manages the coagulant system, a sump and a pump.

Farmers also have the option of a six-year lease at $1832/ month.

The coagulant is an additional cost based on a per litre charge. For a 550-cow farm, milking twice-a-day over a 270- day season it’s likely to be $8000-$9000/year.

The control system telemeters information to computers located in Dunedin to monitor the process and the smart technology allows for two-way communication so inline adjustments can be made as necessary.

The volume of coagulant is monitored that way too so deliveries are automatically scheduled.

Carl says there’s been strong interest in the technology with several systems ordered.

The reduction in the amount of effluent produced is driving a lot of that interest along with the ability to reduce the amount of freshwater used in washdown.

In some areas the dramatic drop in bacteria has prompted orders with more stringent rules for farms now in drinking water allocation zones – or areas within which town drinking water takes are located.

Coagulating the solids

Lincoln University professors Keith Cameron and Hong Di were behind the scientific development of the ClearTech system for farm dairy effluent which uses a coagulant to separate out clarified water from the effluent.

At the same time the process virtually eliminates some bacteria and drastically reduces the amount of soluble phosphorus.

Together with others on their research teams the pair have now published three scientific papers.

They found Eschericia coli (E. coli) levels in the clarified water were reduced by 99.9%, dissolved reactive phosphorous (DRP) was cut by 99% and total nitrogen slashed by 70%.

The treated effluent that remains also has lower levels of potentially harmful elements with E. coli levels down by 91% and DRP down by 99%.

The coagulant, ferric sulphate, is also used in municipal drinking water treatment so poses no potential risks when it comes to being used with farm dairy effluent.

When it mixes with the water in the farm dairy effluent the coagulant sets up a sweep floc motion causing the colloids or solid particles in the effluent to come together, sweeping down and around until they settle out at the bottom, leaving clarified water at the top.

E. coli bacteria are both trapped between colloid particles and killed through a weakening of their cell walls while a chemical reaction saw the phosphorous kept in a form that’s less likely to be lost from the soil.

This article is free to view because it is a topic of high importance. This article was published in New Zealand Dairy Exporter magazine. For less than $10/month, you can receive this detailed information to help improve performance within your business. 
Supporting New Zealand journalism.