Enhanced energy capture, improved dewatering and thermal hydrolysis are just a few of the hot topics to have emerged in biosolids in recent years, according to a veteran of treated sewage sludge research.
Virginia Tech Professor of Civil and Environmental Engineering John Novak has spent more than 40 years researching various aspects of the biosolids process, including anaerobic digestion, dewatering and biosolids storage.
He will be in Australia for the AWA/ANZBP Biosolids National Conference in Brisbane next year, where he will present a keynote address on the future of biosolids research. This includes the growing interest in co-digestion, where food waste is added to the anaerobic digestion process to enhance methane production.
“This is a very hot topic right now – there is a lot of interest in developing methods for the characterisation of food waste,” Novak said.
“This includes energy content, pretreatment and handling problems, and impacts on the final product. There is a lot to learn and this will likely be a focus for the next 10 years.”
Novak will also circle back to where his career began by looking at the renewed interest in improving the dewatering process.
He said the wastewater treatment industry had relied on belt presses and centrifuges for the past 30 years, but that the search is on for a better way of doing things.
“This is where I started with my work on water plant residuals in the 1970s, but it continues to be of interest,” Novak said.
“New dewatering devices have not found widespread acceptance, but we are interested in reducing the conditioning cost and increasing cake solids without increasing the cost of the dewatering devices.”
Thermal hydrolysis – where high temperature and pressure is used to partially dissolve sewage sludge – is also a growing area of interest, particularly for larger utilities. Novak said he believes technological advances will soon open this up to medium-sized businesses as well.
“Basically any utility that uses anaerobic digestion could be interested in some type of thermal hydrolysis system,” he said.
The big stink: Biosolids’ image problem
Australia produces about 327,000 dry tonnes of biosolids each year. This is used for a variety of land applications, including improving agricultural soil and rehabilitating land, for example at former mine sites.
The production of biosolids also generates energy, which can help transform wastewater treatment plants from energy consumers to energy producers.
But while water professionals tend to celebrate the role of biosolids in the circular economy, Novak said treated sewage sludge still has something of an image problem among the general public.
“Professionals in the field view biosolids in terms of resource recovery, but the public views it in terms of some nasty and highly hazardous material,” he said.
A large part of the issue, according to Novak, is the smell. Much of his research has focused on odour and anaerobic digestion, and he said he believes solving the odour problem would help address biosolids’ image issues.
“We are producing methane in order to reduce energy requirements for wastewater treatment and view the final product as a beneficial material for land application,” he said.
“However, the public is concerned about the contaminants in biosolids and the creation of foul odours.”
Novak said it is important to address this as “biosolids management is one of the most important aspects of wastewater treatment”.
“The cost of biosolid treatment and hauling is a major expenditure for wastewater treatment utilities,” he said.
“Pathogens and odour problems may restrict the biosolids disposal options and affect hauling costs.”
John Novak will be presenting at the AWA/ANZBP Biosolids conference in February 2019. To learn more and to register, click here.