Friday, 11 October 2019

In The Field, number 03: Beneficial use of domestic waste

The first post in this series was published on 24 November last year. The post you are reading is an abbreviated version of a story that may, in future, be published on my personal website. Research for the story was performed in April and May 2012 after which publication was halted when the commissioning magazine closed.

In Sydney in the 1980s, “Bondi trout” was a term redolent with meaning. Sydney’s waste had been piped to Bondi since the 1880s, a time when, over a period of 10 years, the city’s population grew from 220,000 to 750,000 and, “the old and very primitive sewerage system was breaking down under the increased load,” wrote architect Morton Herman for his 1956 book, The Architecture of Victorian Sydney.

“There was a period there where before they built the ocean outfalls, where they were discharging sewage at the cliff face,” said Paul Darvodelsky, who at the time was managing director of Pollution Solutions and Design. Our interview was conducted by telephone in April 2012. “When we say at the cliff face, it was a metre off. And it was horrible.”

Tim Moore who, from 1989 to 1992, served as environment minister in the Coalition government led by Nick Greiner, made a statement on the news one day in 1990 that Sydney would not discharge any more sludge into the ocean. In future it would be treated to remove most of the waste and then the resulting liquid would be piped to outfalls placed, at the bottom of the ocean, away from the coast.

The challenge

What to do with the solid waste that would remain on land became a question for managers and scientists, initially within the NSW Environmental Protection Agency. Then within NSW Agriculture (now part of the Department of Primary Industries), which developed a guideline.

“What they did then was develop a document and they looked at the US regulations and they took all available Australian research and fed that in,” said Darvodelsky. “It all went through that and it went through a stakeholder process, and they came up with a document. They also identified shortcomings with the US regulation and ended up with a regulation which was actually much stricter than the US regulation.” Each state developed its own regulations, beginning in 1997 with New South Wales.

While producing viable material was achievable you then had to convince farmers to use it. But the cost of managing biosolids produced by is largely assumed by municipal water authorities.

The Australian Water Association (AWA) said that the average cost for biosolids management was in the order of $300 per dry tonne but Darvodelsky said it was more like $700 per dry tonne. Added to that cost for water managers was the cost of disposing of biosolids, which Darvodelsky said was about $300 per dry tonne. It is given to the contractor at the treatment plant gate. “The range of that is $150 to $500.” Then there are transport costs.

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) estimated the value of biosolids to farmers to be between $66 and $300 per dry tonne. “Beneficial use costs are almost always expressed in cost-per-wet-tonne, or as-is, and the average cost is about $75 to take it from the treatment plant and have all the systems and management in place to reuse it,” said Darvodelsky. “They’re getting less than $5 per [wet] tonne back from the farmer.” Wet tonnes – “as they’re working with it” – are about five times larger than dry tonnes.

The solution

Darvodelsky said that biosolids don’t command much of a price at the farm gate because of the inconvenience. In 2012, Brendon Clarke Arkwood Organic Recycling out of Gatton, in southeast Queensland, was charging farmers $2.50 per wet tonne.

Arkwood sources biosolids from coastal communities from as far south as the Tweed and up as far north as Noosa. “All up it comes to about 340,000 [wet] tonne a year,” Clarke told me in May 2012 on the day I met him in Cecil Plains, west of Toowoomba, in southern Queensland.

The following photo shows an Arkwood spreader applying the biosolids to a field owned by Cecil Plains cotton and grain farmer Graham Clapham. The biosolids are trucked to the field where they are to be used and dumped on the ground. A front-end loader is used to tip them into the hopper. At the back of the hopper two toothed screws spin rapidly, flinging out the material so that it lands on the soil.

There are strict regulations controlling how biosolids can be used and a 2009 report (Australian and New Zealand Biosolids Partnership - Review of Biosolids Guidelines) put out by the AWA says that the higher the quality of the biosolids, the fewer restrictions are placed on their use.

Clapham manages the nutrient levels in his fields and applies biosolids to his crops “when the opportunity presents itself”. “It mineralises quite fast,” said Professor Mike McLaughlin, of the University of Adelaide. “You do get an immediate benefit and a residual benefit for up to two or three years after.” 

Clarke said you get higher crop quality with biosolids compared to using inorganic fertiliser. “There’s a massive difference. On your best soils like these black soils here, you normally end [up with] around a 20-percent better yield, or your quality – particularly with protein in grain – is higher, is quite a lot higher, without exception. It’s always the case. As your soil quality declines – so when you go out [west from Cecil Plains] towards Milmerran, on your lighter soils, or the other side of Cecil Plains – the proportion of increased yield goes up. So, you start around that 20-odd percent on this type of soil [and] we have seen as much as 300 percent, on poor-quality soils, particularly down the east coast.”

“We run a program on our farm that we call nutrient bank,” Clapham said. “It’s a self-made thing, I guess. We do it in conjunction with our agronomic advisor. What that enables us to do is to keep track of the nutrient levels in our soils without actually physically testing them, you know, taking a soil profile and getting it analysed. 

“So, what we do is we have a starting point of what’s in there. Sometimes that’s determined by soil analysis. And from then on – and we’ve been doing this for probably eight years now – we keep track of what we put on and we keep track of what comes off, and there’s a little bit of basic knowledge and a bit of science around mineralisation and effects of floods and effects of irrigation and that sort of stuff. And we’ve got it down to a pretty fine art.” 

The following photo was taken of some of Clapham’s cotton plants growing at the side of a field. Clapham was harvesting the crop on the day I visited his farm, which relies solely on water from precipitation.

No comments: