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Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.

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Cleaner Production - On-site Neutralization of Laboratory Wastewater

Northern Territory University

The Northern Territory University's Faculty of Science designed and installed a 'Neutralization Pit' as a cleaner production initiative. The primary objectives of the University in adopting this form of treatment for the chemical wastewater generated by the Faculty of Science were to:

  1. Prevent pollution and eutrophication of the receiving Darwin watercourses as untreated waste water particularly water containing chemical wastewater compounds can cause significant environmental and health/safety problems or, alternatively
  2. Reduce the University's financial costs associated with waste treatment. Specifically the neutralization system eliminates the need for the employment of waste contractors to treat and dispose of the generated wastewater.

The Neutralization System consists of a series of reaction filter chambers, which raise the pH of their industrial standard wastewater prior to discharge to sewer. The quantity of the wastewater is significant and is generated from the 11 laboratories contained with the Faculty of Science. The neutralization system treats on a daily basis alkaline and acid waste streams, stabilizes BOD and settles heavy metals. The adoption of the neutralization pit, which was modified and designed to fulfil the needs of the Faculty of Science, provides the best possible form of wastewater disposal and treatment in terms of the environment and cost. The payback period for the initial outlay of $9000-00 was approximately 3 years.

Background

The Northern Territory University was established in Darwin on 1 January 1989 through the amalgamation of the University College of Northern Territory and the Darwin Institute of Technology. The University offers both higher education and vocational education and training to meet its first priority of providing for the full spectrum of the tertiary education and research needs of the Northern Territory. The Faculty of Science provides for both Undergraduate and Postgraduate Awards in areas such as Aquaculture, Environmental Biology, Biochemistry and Geographic Information.

The process

The Faculty of Science through their research activities and their Award Programs produce a significant quantity of chemical wastewater. Prior to the adoption of their cleaner production initiative, the chemical wastewater was collected, treated and disposed of by a waste contract service. Given the significant quantities of wastewater produced, this option for collection and disposal proved to be extremely costly. Direct discharge to sewer provides the most economically viable option for the laboratory wastewater of an acceptable of standard. Despite the Faculty of Science's wastewater undergoing minimal pre-treatment within the laboratories prior to disposal it did not attain the acceptable pH standard for direct discharge to the Power and Water Authority (PAWA) sewer.

For wastewater effluent to be discharged directly to the sewer, the pH should generally not be lower than 6.5 and not higher than 11. The acid and alkali waste streams that do not occur within this range have the potential to seriously affect the pH value of the receiving water if they are discharged directly without acceptable pre-treatment. The acid wastewater reacts with the alkalinity of the receiving water by:

Ca (HCO3)2 + 2HCl = CaCl2 + 2H2O + 2CO2

Alkalis react with free carbon dioxide dissolved in the receiving water and increase its alkalinity by:

2NaOH + CO2 = Na2CO3 + H2O

If the Faculty of Science had discharged its wastewater directly to sewer and had not adjusted the reaction of the pH, then the following problems would have occurred:

  1. Biocoensis as both animal and plant organisms perish in excessively acid and excessively alkaline media.
  2. Damage to PAWA sewer lines and plant structures from untreated effluent that would corrode both concrete and metals.
  3. Alkalis have the potential to cause serious difficulties in the operation of the receiving treatment plant. Sealants used in conduits may be attacked by alkalis, causing leakage and damage in the network as well as causing precipitation of various deposits and hence choking of the pipes.
  4. Increased demand for excessive chemicals necessary for coagulation when employed as a treatment method;
  5. Insufficient provision for optimum bacterial activity in the biological treatment of wastes;
  6. Production of noxious odours which may emitted at low or high pH values;
  7. Damage to the receiving Darwin waters and environs due to the detrimental effects of the Laboratory wastewater.

Conscious of the possible detrimental impacts of the untreated wastewater and the increasing cost of employing a waste contract service, the Faculty of Science identified the need to install their own treatment system which could be utilised so as allow for appropriate standard of direct discharge to sewer. The primary function of such a treatment system would be to neutralize the acidity or alkalinity of the Faculty's wastewater and in turn reduce the costs of treatment.

Cleaner production initiative

The Faculty of Science at the Northern Territory University installed a 4500 litre neutralization pit as their cleaner production initiative to treat the significant volumes of wastewater generated by the 11 laboratories located within the Faculty of Science. The process of neutralization is best defined as the process by which acids and alkalis can be rendered harmless and the degree of neutralization can be measured in numerical terms through the system known as pH (hydrogen ions). Thus the Faculty's neutralization system treats on a daily basis alkaline and acid waste streams, as well as stabilises the BOD level and settles heavy metals.

View Graphic

Figure 1
Typical Section of the Neutralizing Pit

The Faculty's neutralisation pit consists of a series of reaction filter chambers, which raise the pH of their industrial standard wastewater prior to discharge to sewer. Figure 1 is a schematic drawing of the Neutralization Pit that the Faculty of Science has installed. The raw material that the pit uses is limestone. The limestone is utilised in chip form and is distributed within the 4 reaction chambers to neutralize the moderate acid and caustic wastes. By putting the wastewater stream through the limestone bed of the neutralization pit, the acid components of the effluent react with the calcium carbonate of the lime, to form harmless neutral salts, carbon dioxide and water. The neutral salts precipitate into sludge and settle to the bottom of the neutralization tank. Carbon dioxide gas mixes with water to form carbonic acid, which helps to neutralize the alkaline (caustic wastes). The water within the neutralization pit helps to further dilute the acidic, alkaline and solvent wastes.

The chemical reaction is as follows:

2HCI + CaC03 <->CaCL2 + CO2 + H20

CO2 + H20 <-> H2CO3

2NaOH + H2CO3 <-> NaCO3 + 2H20

Where

HCl = hydrochloric acid CaCL2 = calcium chloride H20 = water
H2C03 = carbonic acid CaCO3 = calcium carbonate CO2= carbon dioxide
NaOH = sodium hydroxide Na2CO3 = sodium carbonate

The adoption of the neutralization pit, which was modified and designed to fulfil the needs of the Faculty of Science, provides the best possible form of wastewater disposal and treatment in terms of the environment and cost. Thus this technology has proven to be a successful cleaner production initiative of the Northern Territory University as their laboratory wastewater achieves the required pH levels suitable for direct discharge to sewer.

Advantage of the process

Neutralization of the potentially hazardous laboratories wastewaters is necessary, even when the quantities and concentrations are small. The Faculty of Science identified that if the pH of the laboratory wastewater was left untreated significant damage would occur to the PAWA infrastructure and the receiving Darwin environment. Therefore, by undertaking neutralization for the treatment of generated wastewater, the following advantages have been gained:

  1. The prevention of pollution and eutrophication of the receiving Darwin watercourses as untreated waste water particularly one contained chemical wastewater compounds would have caused significant environmental problems and health problems;
  2. The system has eliminated the need to employ waste contractors to treat and dispose of the generated wastewater off site;
  3. Marked reduction in the costs associated with waste treatment. Specifically the neutralization system has reduced the raw material costs by utilising the low cost material, limestone chips for pre-treatment. Alternative chemical treatment previously employed was an expensive and unfeasible option.

The Northern Territory's Faculty of Science willingly adopted the neutralisation system as their cleaner production initiative. They have easily justified the installation and operational costs given the direct benefit of achieving the receiving water quality standards and the elimination of nuisances to the environment. Table 1 contains the costs and savings associated with the adoption of the neutralisation pit as a cleaner production initiative.

Table 1
Costs and Savings

ECONOMIC BENEFITS
Costs  
Capital Cost of Neutralization Pit $9000-00
Annual Savings  
Disposal Fees & Chemical Treatment $3000-00
Total Annual Savings
Payback Period
$3000-00
3 years
  • Purchase Price for the Limestone Chips when replaced in 5 years
  • will be $200-00 per annum.

Cleaner production incentive

The main incentive for adopting the cleaner production practice was the Northern Territory University's ongoing commitment to minimising the impact of their activities on the Darwin environment.

Barriers

No barriers were encountered in implementing this simple cleaner production initiative. The Northern Territory University is committed to the environmentally responsible activities/actions, which incorporates the principles of sustainable development without jeopardising public safety or the security of their infrastructure assets.

Further development

The Northern Territory University is continuing to benefit from this initiative.

Contact

Steve Beagley
Head of Works
Northern Territory University
Ellen Gowan Drive
Casuarina NT 0810 
Ph: 61 8 8946 6606 
Fax: 61 8 8946 6562
steve.beagley@ntu.edu.au

Date of implementation: 1995.
Date of further initiatives: Ongoing.
Case study prepared 1997 by Northern Territory Chamber of Commerce and Industry in conjunction with the Northern Territory University.
Date last modified: May 2001.