https://www.engineeringnews.co.za

Home-grown bioremediation process turns harmful industrial sludge into fertilisers

30th January 2015

By: Schalk Burger

Creamer Media Senior Deputy Editor

  

Font size: - +

Petrochemicals giant Sasol, which typically incinerates its waste sludge streams or sends them to hazardous waste sites, is increasing its use of composting to treat these streams at its Secunda plant, in Mpumalanga, reducing transportation and disposal costs, as well as air pollution.

Composting has been developed as a detailed and controllable industrial process that has proven to effectively treat oily industrial waste sludges using a combination of various bacteria and fungi, says Sasol Technology environment technology manager Dr Sarushen Pillay.

The industrial sludges derive from the plant’s wastewater treatment processes that use aerobic microbes to capture contaminants in the wastewater, as well as sludges from the bottom of cooling towers. The water is recycled as process water.

The contaminated sludges are then concentrated, but 90% of the volume of the sludge streams incinerated remains water, making incineration an energy- intensive process.

“Secunda was designed as a zero-discharge plant. All our used water and rainwater runoff is captured in dams, where residual oils are skimmed off and then treated to be reused. However, meeting this requirement increased costs and, with the new air quality regulations coming into effect, we aimed to use our knowledge of chemical processes to address these twin challenges,” Pillay says.

Composting is extensively used in sewage wastewater treatment operations, especially internationally, but the oily organic compounds of the Secunda plant’s wastewater are much more difficult to break down than sewage sludge and composting of industrial sludges has not been done before on an industrial scale.

“The microbes used in the Secunda Bioworks wastewater treatment plant can treat streams that contain phenols, which have antibacterial properties, and ammonia, a commonly used cleaning agent. The success of the Bioworks gave us the confidence that an effective composting process using bacteria could be designed to treat the compounds in the sludges.”

Bioremediation company Sola Fidei Manufacturing, established under Sasol’s supplier development initiative, has developed a method to activate specialised microbial populations, specifically heavy-metal-composting bacteria, to target, assimilate and biochemically transform the trace elements in industrial waste sludge into immobilised and environment-friendly forms.

Biochemical Pathways
A key factor in designing industrial bioremediation processes is determining the composition of the bacterial populations that can collectively treat the complex compounds and convert the industrial sludge into fertilisers, says Sola Fidei Manufacturing junior manager Rudi Pretorius.

“The microbes require the biochemical pathways to be able to absorb the contaminants and biochemically convert them into less hazardous forms. “Therefore, we had to select microbes and condition them to be suitable for the unique feed streams considered for this composting project.”

Microbes are ideally suited for the process because they can survive the contaminant levels present in the feed sludge.

The microbes are conditioned in such a way that, prior to addition, they can grow rapidly in the specific composting conditions, which enable them to effectively transform the sludge streams, Pretorius explains.

Volatilisation and methylation are used during the composting process to treat the residual heavy metals and toxic compounds, and render them inert, says Sasol Secunda assistant technology manager Candice Odell.

Methylation of heavy metals changes their solubility, volatility and reactivity, enabling them to be absorbed safely by plants grown using the compost. Volatilisation of heavy- metal-containing compounds leads to the compounds being vaporised and entering the atmosphere. A similar, but uncontrolled, process occurs at landfill sites worldwide, she notes.

Environmental methylation is a significant factor in the movement of heavy metals in natural systems and is also linked to volatilisation, as it frees heavy metals and contaminants from organic lattices, enabling them to be volatised.

“Despite the complex chemistry, this system has been developed into an industrial process that can be manipulated to treat a variety of waste sludges and contaminants,” explains Pillay.

The most difficult compounds to convert are heavy oils and tarry components. Different strains of bacteria are required to treat the different waste streams. Each bacterial species is used to target specific chemical compounds or related groups of compounds, with some breaking down heavy hydrocarbons and others converting other contaminants.

However, some of the microbes do not feed directly on the compounds in the sludges, relying instead on the waste products of some of the other bacteria, which contain intermediate species of contaminant chemicals, as a source of food, which highlights the complexity of characterising and designing microbiological processes.

Sasol uses a bulking material to provide a ready food source for the bacteria and fungi while they also convert the contaminants in the sludges into less hazardous forms.

The bulking materials are grown without irrigation on 2 000 ha of unused land around the Secunda plant using the fertilisers derived from the industrial sludges. Sasol is growing sugar graze – a hardy, fibrous plant commonly used as cattle feed.

Multiple tests were done on the soil and the plants’ roots, stems and leaves before and after the fertilisers from the composted industrial sludges were applied and no abnormal concentrations of heavy-metal compounds or toxic compounds were found, says Pretorius.

Odell notes that Sasol has been testing and piloting the process since 2012. “We applied the strictest composting regulations in South Africa during our trials. However, this was a new process, so we did a battery of additional tests on air, soil and water quality, as well as on the fertilisers and bulking material plants grown with and without the resultant fertilisers. We used the results from these tests to improve the process.”

The composting process is controlled by means temperature and aeration, which is achieved by turning the windrows. The final step in the process, after about 12 to 14 weeks, is to let the temperature of the windrows rise above 65 ºC, killing the bacteria and sterilising the compost.

The amended Waste Act and the new Air Quality Act introduced more stringent emission standards and significant penalties for transgressors, which added impetus to this composting project.

“However, the overarching objective behind these regulations is to reduce pollution and divert waste away from landfill and up the waste value chain to reduce the negative environmental and social impacts, as well as the costs of disposal and treatment, while bolstering the reuse of materials where possible.

“The fertilisers produced by the composting process are used to grow the bulking materials used in the process, making the whole process carbon neutral and self-sustaining. “The process also reduces air pollution and greenhouse-gas generation significantly, compared with incineration. It also leads to less waste being sent to hazardous waste sites,” says Pillay.

The regulations are already having an impact on industries and new methods of addressing their stipulations efficiently are required without impacting adversely on prices and competitiveness.

However, all plants, existing and new, will have to meet the new Air Quality Act regulations. Extensions only afford the companies affected an opportunity to implement initiatives to meet these standards, notes Pillay.

Further, the compost produced could potentially be used for a variety of remediation programmes, including the remediation of ash heaps. In terms of other industrial applications, Sasol is tracking developments in biotechnology.

“Sola Fidei Manufacturing was able to process a wider variety of feed streams than initially anticipated. Further testwork on additional streams is planned for the next phase of the project.

“So far, testwork has been carried out only on Secunda waste streams, but the plan is to extend this work to other Sasol sites to investigate whether the technology will be suitable,” concludes Pillay.

Edited by Creamer Media Reporter

Comments

Latest News

An image of Maltento CEO Dean Smorenburg, Cape Town mayor Geordin Hill-Lewis and Cape Town premier Alan Winde
Maltento aiming to bolster sustainability efforts
18th March 2024 By: Tasneem Bulbulia

Showroom

Weir Minerals Africa and Middle East
Weir Minerals Africa and Middle East

Weir Minerals Europe, Middle East and Africa is a global supplier of excellent minerals solutions, including pumps, valves, hydrocyclones,...

VISIT SHOWROOM 
Universal Storage Systems (SA)
Universal Storage Systems (SA)

South African leader in Steel -Racking, -Shelving, and -Mezzanine flooring. Universal has innovated an approach which encompasses conceptualising,...

VISIT SHOWROOM 

Latest Multimedia

sponsored by

Photo of Martin Creamer
On-The-Air (15/03/2024)
15th March 2024 By: Martin Creamer
Magazine round up | 15 March 2024
Magazine round up | 15 March 2024
15th March 2024

Option 1 (equivalent of R125 a month):

Receive a weekly copy of Creamer Media's Engineering News & Mining Weekly magazine
(print copy for those in South Africa and e-magazine for those outside of South Africa)
Receive daily email newsletters
Access to full search results
Access archive of magazine back copies
Access to Projects in Progress
Access to ONE Research Report of your choice in PDF format

Option 2 (equivalent of R375 a month):

All benefits from Option 1
PLUS
Access to Creamer Media's Research Channel Africa for ALL Research Reports, in PDF format, on various industrial and mining sectors including Electricity; Water; Energy Transition; Hydrogen; Roads, Rail and Ports; Coal; Gold; Platinum; Battery Metals; etc.

Already a subscriber?

Forgotten your password?

MAGAZINE & ONLINE

SUBSCRIBE

RESEARCH CHANNEL AFRICA

SUBSCRIBE

CORPORATE PACKAGES

CLICK FOR A QUOTATION







sq:0.178 0.246s - 156pq - 2rq
Subscribe Now