A silk purse from a sow's ear

BY RICHARD WOODD

Taranaki pig farmer Steve Lepper has built a covered effluent pond that almost entirely eliminates atmospheric odour and produces enough methane to fuel a generator.

He's the first New Zealand pig farmer to go the whole hog on effluent management with what could become an industry model. The piggery is a farrow-to-finish operation. There are 400 resident sows producing about 9500 offspring per year, which are grown for the Auckland fresh market.

They eat about 2000 tonnes of meal per year, all ground and mixed on the premises from milk powder, barley, wheat, palm kernel, soya bean, minerals, vitamins and amino acids, cooked chicken offal and reject bread.

Management and disposal of their solid and liquid waste is a major challenge for Steve and his staff of six.

For the past 40 years, since it was built by his father, Dennis, the large-scale commercial piggery has been storing its effluent in two open oxidation ponds close to Lepperton.

Complaints from downwind residents about odours had increased to the point where "I had to do something about it in order to keep pig farming, otherwise I'd have been fined out of existence. That's the reality," Steve says.

The ponds, shared with his brother Graham's dairy shed effluent, are still used, but the pig effluent now passes through a covered anaerobic biogas digester that removes most of the hydrogen sulphide, which causes the offensive smell.

The effluent is contained in a 60 metre by 20 metre by 7 metre deep pit. The pit capacity is 7200 cubic metres. The cover went on in May 2009 and the gas generation system was commissioned in late January.

Methane gas rises and is trapped under the heavy, seam- welded plastic cover (guaranteed to resist ultraviolet radiation for 20 years). In warm weather, the cover balloons out, with up to 1200 cubic metres of gas beneath it.

The gas is compressed and forced through a hydrogen sulphide scrubber to a converted six-cylinder diesel engine that spins a 40 kilowatt generator. This is producing half of the piggery's electricity from about 200 cubic metres of gas daily.

Heat exchangers on the engine cooling system and exhaust are heating enough water to eventually warm the entire piggery with under-floor heating pipes, allowing Steve to eliminate costly radiant lamps.

A 9000-litre tank of water is being maintained at 50[Degree]C from exhaust heat and the volume could easily be doubled.

The hot water will also be used to improve the efficiency of the in-house mains gas-fired boiler, which supplies heat for waste offal cooking to produce a protein meal for the stock.

The piggery's monthly power bill is $6000-$7000, depending on the weather, and Steve expects to recover his $100,000 investment within three years (the Energy Efficiency and Conservation Authority helped out with a grant of $30,000). There is potential to sell surplus power back to the grid.

"We've been working on this complex project for two years and although it's still early days, it is looking very promising," he says. "It's been a major learning curve for me and I'm grateful for the input of many different people around the country who offered some real Kiwi ingenuity to make it all work."

His original concept was to build a huge flexible cigar in the ground, which would receive industrial food waste from all around Taranaki, using the gas from that to generate electricity and heat.

"But it became too complex, the waste streams were too small, it would cost millions of dollars and in the end, all I would be doing was bringing other people's waste problems on to my property. So I decided to keep it simple and just deal with my own."

The biogas digester is the final phase of the D.H. Lepper Trust's plan to move its operations away from the residential area and introduce serious odour- reduction technology to the plant.

In 1985, the piggery was moved to high ground in the middle of the family dairy farm. Processed effluent continued to be gravity-flowed to the ponds two kilometres away, which discharge into a tributary of the Waiongana River when it rains heavily.

After the relocation, the piggery began screening out solid waste. This is mixed with sawdust, composted and sold at the gate in bags as a soil conditioner under the brand Grunt. It sells out every year, despite never having been advertised.

The new digester and gas co- generation has been Steve's baby and the results have so far received positive ticks from environmental consenting authority Taranaki Regional Council. The council has the piggery under close scrutiny and adopted a supportive attitude to the latest development.

The piggery discharges are controlled by special conditions attached to its water-discharge, water-abstraction and air-discharge permits.

The latest TRC report comments: "Lepperton, like many small rural towns in New Zealand, is going through a period of change. Land that was used for dairy farming is now being subdivided into smaller lots and, with the inevitable increase in population, attitudes change, forcing existing farmers such as pig and poultry growers to adapt to new regulatory conditions."

Key features of covered anaerobic ponds were listed as:

Low-cost, advanced design.

Simple operation and maintenance.

Elimination of odours, flies and insects from the pond.

Prevent rainwater intrusion and enable collection for beneficial use.

Enhanced treatment performance and biogas production.

Economically recover biogas energy.

Reuse treated effluent for washdown.

Storage for deferred irrigation.

Reduced odour from effluent irrigation (by as much as 70 per cent).

Reduced GHG emissions and potential for carbon credits.

Increased microbial activity in the anaerobic pond, producing a cleaner waste water discharge.

"Whether covering an existing pond or developing from scratch, anaerobic ponds are an extremely cost-effective way of utilising anaerobic digestion technology," the report says.

"They are more suitable for larger piggeries, dairy farms, meatworks and other agricultural processing plants needing to optimise anaerobic treatment and capture renewable energy while reducing greenhouse gas emissions."

Steve fears his apparently successful solution to fundamental environmental issues of piggery operation may become a standard.

"If this works, I don't want regional councils going to pig farmers who don't have environmental problems saying: you must put this in.

"This is a solution to our problem. Each situation is different."

- © Fairfax NZ News