Chemical fixation, solidification of hazardous waste

Chemical fixation, solidification of hazardous waste

Waste Management & Research (1990) 8, 105-111 CHEMICAL FIXATION, SOLIDIFICATION OF HAZARDOUS WASTE W . E . Razzell* (Received September 1989) Effici...

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Waste Management & Research (1990) 8, 105-111


(Received September 1989) Efficient, cost effective measures for the safe disposal of hazardous wastes have been developed to meet the needs of industries in Brisbane and the surrounding area . Liquid hazardous wastes are neutralised, oxidised, or reduced as appropriate, and fixed (solidified) by the addition of fly-ash and cement kiln dust to form a material of the consistency of coarse gravel . Fixation is performed in cells dug in solid clay, holding about 70 tonnes . Fixed material containing pesticides, paints or organic solvents is left in the clay cells, capped with clay ; fixed inorganics and waste oils having no toxic contaminants are used for land contouring on the site . Leachate tests on the latter have been uniformly below 10 times USEPA Drinking Water guidelines - that is, 10 times better than the limits nominated by the EP Leach Test (1980) . Bores around the site have detected no leachates during the past seven years . A simple but effective management system keeps wastes segregated and confirms the identity of each batch of waste on receipt . All costs are charged to the waste generator including costs of correcting errors . Key Words-Hazardous waste, fixation, solidification, cement, flyash, leachate, management system, Australia .

1 . Introduction Low-cost technology for treatment of hazardous wastes backed up by prompt analytical services has been applied in Brisbane since 1982 . In conjunction with good quality clay ground for permanent burial of some wastes, the procedure can be applied to any liquid waste, at an average cost of 10 cents litre - ' - not including land acquisition costs for the site of treatment and disposal . The process relies on solidification of liquid wastes with flyash (a waste from dust emission control at coal-fired power stations) and cement kiln dust (a waste, similarly, from cement manufacturing) . All treatments are conducted in clay cells of 40-70 tonne capacity, at ground level . With non-biodegradable wastes segregated into seven classes at the sources, and during transport to the treatment site, most solidified waste products pass the USEPA (1980) Leach Test, yielding leachates containing less than 10 times the drinking water standard for proscribed constituents . However, oily wastes, and pesticide, paint and solvent wastes leach appreciably because the constituents are not bound in chemical combination . The treated pesticide, paint and solvent wastes are left in the clay cells in which they are created, the cells being capped with clay to exclude water . 2 . The problem The various non-biodegradable wastes (those that cannot be treated in the sewage

*Dr . Wilfred E . Razzell, Director of Scientific Services, Brisbane City Council, Donaldson Road, Rocklea 4106, Queensland, Australia. 0734-242X/90/020105 + 07 $03 .00/0

0C 1990 ISWA

1 06

W. E. Razzell

treatment system) commonly seen in the disposal system (as distinct from any established recycling or recovery system) are : Class 1 . Class 2. Class 3. Class 4. Class 5. Class 6. Class 7.

oily water (with tetraethyl lead) ; oily water (with solvents, phenols, alkali) ; metal stripping acids (rust, hydrochloric acid, iron chloride) ; metal finishing acids (plating bath washes) ; metal finishing alkali; pesticides and toxic organic compounds ; and special (chromates, arsenic, cyanide, etc .)

If these waste classes are segregated at the premises where they originate, and not mixed during transport, then the handling and treatment of them can be safe and rational . In Brisbane, and in the surrounding communities which use the waste management system (population 1 .7 million), about 13 million litres of hazardous wastes are treated each year by the Industrial Liquid Waste Treatment Plant (ILWTP) at a total cost of about $1 M U .S . The population of Queensland is about 2 .6 million, with the majority of chemical industry in and around Brisbane . Waste arisings in the rest of the State are unknown and no system exists for their management . Whereas distances within the Brisbane management system are reasonably short (a maximum of 40 km), the distance from Brisbane to Cairns, also in Queensland, is 1000 km . 2.1 Brisbane

Environmental quality in the area is generally excellent . As there is a good supply of surface water sources for domestic and manufacturing uses, the groundwater which is frequently brackish is used only for agricultural irrigation - if at all . In the years prior to 1981, complacency and expediency had led to widespread dumping of hazardous wastes, some consequences of which are only beginning to surface . The site now used for hazardous waste treatment, for example, is riddled with old trenching areas and buried containers . 3. Developing management In order to effect control, in Brisbane all industrial premises are visited by Brisbane City Council's trade waste control officers (chemists) who assess the processes being used and the wastes generated . Wastes which will not harm the sewers, sewerage workers or the secondary treatment plant processes are accepted into the sewer system . The cost relates to volume, composition and concentration (BOD above 600 ppm costs $0 .10 kg', hydrocarbons and oils or chromium must not exceed 20 ppm, etc .) . When a waste generator cannot put his waste into the sewer, he must arrange an analysis and an approval from Scientific Services - including such segregation as may be required - and each class of waste requires the generator to have a separate Approval Number. Trade waste control officers inspect each major waste generator at least once per year, unannounced and without interference . Lesser generators are also checked at random ; an unapproved change, when discovered, is charged for on the assumption it has prevailed since the previous inspection . Major sewer connections are sampled periodically to ensure that limits are not exceeded . The treatment/disposal pricing schedule is based on total "polluter pays" recovery : all administrative, field staff, record-keeping, testing and analysis, office/laboratory accom-

Chemical fixation and solidification


modation, facility depreciation, treatment and site monitoring costs are built into the prices charged which vary between 5 and 10 C U .S . I ' . The only cost not accounted for is the opportunity cost of the real estate tied up at the site (some 50 ha) . 4. Cradle to grave management The process of moving hazardous waste, mostly liquids, from generator to ultimate disposal begins with an inspection of the industrial premises by a graduate chemist Trade Waste Control Officer . He identifies wastes that can be discharged to the sewer and sends samples to the Scientific Services Laboratory for classification and approval for shipment . When all decisions have been approved by the Director of Scientific Services, the generator is free to select a transporter from among those who have been approved by the City Council to transport hazardous wastes and, if necessary, by the State Transport Department to carry dangerous goods to the Industrial Liquid Waste Treatment Plant (ILWTP) . There is no legal alternative to the ILWTP for hazardous wastes in the State . The transporter charges the generator for both the transport costs (a competitive rate) and the specified ILWTP costs . Transporters must arrange deliveries with the ILWTP at least 48 hours in advance or be charged an extra service fee . On arrival, the transporter's truck is weighed . A sample is taken from the truck and subjected to screening tests immediately to confirm the composition of the load . A docket system is used to confirm that the waste sent by the generator arrives at the ILWTP . The truck is accompanied by a Scientific Services assistant to the designated treatment pit for discharging . If there is any doubt, the truck is discharged to a concrete holding pit . Once full enough (about 70 tonnes for most classes, only 40 tonnes for Class 2 and 6 wastes) the treatment pit is sampled and analysed thoroughly at the main laboratory . If a problem is found, all truck samples are analysed, the source of the problem identified, and that transporter charged with all extra costs incurred in treating the contents of the pit. 5. Solidification procedures Table 1 presents the parameters of classification, analysis and treatment to achieve solidification of various wastes, including annual quantities and unit costs . The total waste stream generally contains an excess of acid and materials requiring oxidation ; therefore alkaline wastes are transported together when they are compatible, and stored on site for use as required, as are oxidising agents (also as a matter of safety) . However, some wastes are too salty or too concentrated to fit easily into the procedures and therefore attract extra charges as well as further segregated transport . Once treated, wastes in Classes 1, 3, 4, 5 and often 7, can be removed from the clay cells in which they have been solidified . This is done about the fifth day after treatment when the solidification has not yet proceeded to rock-hard consistency ; the solids are stockpiled to allow completion of the process over a further seven days . The material is then used to fill depressions, as road base, or as cover material on the site . Cells containing fixed, solidified, wastes in Classes 2, 6 and sometimes 7, are capped with other fixed wastes and 50 cm of good clay, then contoured on the site to shed water .


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TABLE 2 Classes 1, 3, 4 and 5


Total organic carbon Petroleum hydrocarbon Phenol (total) Polychlorinated biphenyls Zinc Lead Copper Chromium Cadmium Nickel Arsenic Selenium Mercury Iron Aluminium Calcium Sodium Cyanide

Leaching characteristics* Max

Desirablet drinking USEPA toxicityl water guideline criteria mg 1 - ' mg I - '

107 < 5

0 .10 < 0 .02 25 0 .5

0 .9 0 .1 <0 .1 0 .3 0 .13 0 .003 0 .005

0 .01 0 .002


15 0 .05 1 .5 0 .05

1500 5 150 5

0 .01


0 .05 0 .01 0 .001

5 1 0 .1

1 .8 30 5300

4700 < 1 .0

0 .20



* Leachate analyses were conducted in accordance with the USEPA EP 1980 Toxicity Test Procedure . Data in mg I - ' . Number of representative runs= 20 . t National Health and Medical Research Council Guidelines for Drinking Water in Australia . $ Maximum concentration of contaminants allowable when characterised using USEPA EP Toxicity Test Procedure (e .g . normally 100 times primary drinking water standards) . Mean values were in general less than one third of the maximum except for calcium and sodium .

6. Environmental/quality controls Table 2 illustrates some of the leaching characteristics of solidified wastes in Classes 1, 3, 4 and 5 . It is evident that the organic hydrocarbons (as Total Organic Carbon) leach significantly, whereas the metals do not ; it is believed that the metals are chemically bonded as ions or oxides in the silicate complexes of the cement, whereas the oils are merely coated : thus the grinding process prior to the leach test provides an opportunity for the oils to escape . The fixation of the metals is effective, whether alone or together with hydrocarbons . The environmental significance of leaching hydrocarbons is minimal : in practice, the leach rate is much slower than in the test, and the compounds are slowly biodegradable at low concentrations . The real significance, of course, lies in the distance downstream to a sensitive target, as well as the rainfall pattern . Over the course of seven years, some 1000 70-tonne batches of waste in Classes 1, 3, 4 and 5 have been fixed successfully without any leach test results exceeding 10 times the USEPA drinking water standards - which is 10 times better than the requirements of the USEPA Leach Test . In almost all cases the heavy metal leachates were below the drinking water standards . Total Organic Carbon is not included in the EPA Leach Test Criteria of 1980 .

Chemical fixation and solidification


Surrounding the fixation cells, the permanent interment cells, and other sensitive areas of our site are 50 boreholes which intersect the groundwater . These are sampled quarterly at the perimeter of the site, and monthly near working areas or sensitive locations . Results over the past seven years show no leaching from working pits or permanent burial areas and no migration away from the site as a whole . 7. Key factors The solidification/fixation process itself requires : • flexibility to blend waste batches to achieve the parameters necessary for good results ; • good analytical backup, promptly provided ; and • control by an experienced, graduate chemist .

The maintenance of low costs requires : • inexpensive land for the site ; • natural clay beds for the pits ; • segregated waste storage and transport to allow wastes to be used to neutralize each other, and to conserve chemicals ; and • inexpensive flyash and kiln dust sources .

The maintenance of environmental quality requires : • • • • •

a registration process for generators ; a control mechanism for transporters; site design and security to facilitate operations ; a thorough site monitoring program ; and inspections and controls by an experienced, graduate chemist .

In the absence of good legislation, an excess of hard work is required . References USEPA (1980), Leaching of Solidified Waste . Federal Register 19 May 1980.

Postscript Although the standards used are admittedly not as tight as those deemed necessary in some countries, particularly where the soils are sandy and overlay drinking water aquifers, there is as yet no evidence that the treatment is causing ecological damage . The cost is low enough to make it acceptable and the possible environmental effects are far less than those caused by uncontrolled dumping . Doing something within our means is far better than doing nothing until a perfect solution comes along .