Co-disposal of industrial wastes with municipal solid wastes

Resources, Conservation and Recycling, 4 (1990) 33-49 33 Elsevier Science Publishers B.V. /Pergamon Press plc - - Printed in The Netherlands

Co-disposal of industrial wastes with municipal solid wastes

P.E. Rushbrook* Environmental Safety Centre, Harwell Laboratory, Didcot, Oxfordshire, 0)(11 ORA (U.K.)

ABSTRACT

Rushbrook, P.E., 1990. Co-disposal of industrial wastes with municipal solid wastes. Eur. Symp. on Integrated Resource Recovery from Municipal Solid Wastes. Resour. Conserv. RecycL, 4: 33-49.

The disposal of solid wastes in landfill sites is often a cause for public concern. This need not be the case. It is argued that upgrading landfill disposal operations to acceptable "controlled" ("sanitary") standards is an essential first step to improve the quality of a solid waste management service in any municipality. Landfill capacity will always be required and hence landfilling should be conducted in the best way possible, appropriate to the standards sought locally.

Good solid waste landfill provides a foundation from which a municipality can develop an ex- panded range of waste management options. These may include mechanised waste treatment, incin- eration, and resource recovery. In addition, the controlled land filling of municipal wastes can provide an opportunity for the safer disposal of many (but not necessarily all) of the industrial wastes which are generated from manufacturing operations.

This paper also calls on international funding agencies to promote and encourage projects on siting and upgrading of municipal and industrial waste landfill operations. Such projects would support and supplement the existing international programmes which promote resource recovery.

INTRODUCTION

Considerable concern has been expressed at national and international levels over the disposal of wastes to land. In the last decade many governments have introduced wide-ranging restrictions on the materials which can be deposited in landfills, or have attempted to ban land disposal completely. All too frequently, these official stances are founded primarily on social consid- erations and often the scientific evidence for such decisions has not been wholly conclusive.

It is argued in this paper that the concept of co-disposal of municipal waste with some industrial wastes in landfills is not wrong, but that in some in- stances criticism should be directed towards the existing design and manage-

*Present address: GIBB Environmental Sciences, Centurion Court, 85 Milton Park, Abingdon, Oxfordshire OX 14 4RY, U.K.

34 P.E. RUSHBROOK

ment of landfill operations. Due to the common public perception that all landfills are nuisances they are treated in the same category as prisons, air- ports and new roads. Everybody knows they need them to maintain and improve the quality of their lives, but nobody wants them near to their home. The Americans have invented an acronym for this, "NIMBY" - Not In My Back Yard.

All human activities produce waste and it is inevitable that some discarded materials cannot be recovered or treated. Hence, they need to be disposed of in a final resting place. This has traditionally been landfill and there remains no large-scale, credible alternative option for final disposal. The use of ce- ment kilns shows some promise but even this method requires the screening- out of non-reducible items, such as large metal objects, carpets, wire and aggregate. Consequently, in addition to the consideration and adoption of some alternative methods to treat and recover proportions of municipal and industrial waste, most will continue to go for ultimate disposal in landfills.

It is suggested that in any project to improve waste management facilities in a municipality, an improvement of landfill design and management should be the starting point. In this way a safer, final disposal route to landfill will be secured and it provides a working basis upon which managers can consider the future adoption of waste reduction, treatment and recovery technologies for municipal, and subsequently industrial, wastes. If landfill operations are not improved they will adversely affect the entire waste management struc- ture being developed in a municipality.

M U N I C I P A L WASTE L A N D F I L L PROCESSES

The typical perception of landfill in many countries is that of a poorly managed dumping operation. Often the sites for such dumps are ill-conceived and the waste placement is nothing more than loose tipping from a collection ve- hicle. These dumps are commonly sources of nuisance, vermin, odour, litter, off-site migration of leachates, disease, and fires.

A description of the underlying waste decomposition processes illustrates the causes of waste management problems at uncontrolled landfills. In the early 1970s the pattern of landfill gas production was first postulated [ 1 ]. This work demonstrated that all landfills have the potential over time to go through five distinct phases (Fig. 1 ).

Phase L Aerobic decomposition

Organic wastes decompose in the presence of oxygen. Putrescible (vegeta- ble and food wastes) materials degrade most readily, followed by paper, wood, natural textiles and rubbers. This phase is characterised by rising carbon dioxide concentrations from aerobic respiration of micro-organisms and rising

CO-DISPOSAL OF I N D U S T R I A L A N D M U N I C I P A L WASTES 3 5

I Landfill gas production pattern Phase

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waste temperatures, derived from accelerating exothermic microbial decomposition processes. Also there are rising carboxylic acid concentrations in leachates formed as products of incomplete metabolic degradation by bacteria. This phase lasts only a few days or weeks in well-run controlled landfills. In poorly run landfills with a low density of waste emplacement and no com- paction this phase can predominate. In these circumstances the landfill will be characterised by high temperatures, strong odours, and high carboxylic acid concentrations in leachates, which could lead to surface and groundwater contamination. Such landfills create a wholly unacceptable impact on the environment and are the most unacceptable type of landfill operation.

Phase H. Anaerobic, acetogenic decomposition

In most landfills oxygen is rapidly depleted and the environmental composition becomes more reducing. Anaerobic bacterial systems take over. This phase will last up to several months at well-run sites, and during this period carbon dioxide concentrations rise to over 70% by volume and carboxylic acid concentrations also continue to increase. This phase is propagated by acid-forming and acetogenic bacteria whose metabolic conversion of cellu- lose produces carboxylic acids (predominantly acetic acid), carbon dioxide and smaller quantities of hydrogen. Some landfills operate at this phase per- manently. On the surface they may appear to be well run, but the waste degradation achieved can produce excessive quantities of high "strength"* leachate containing carboxylic acids. This is principally due to the establishment

*That is, high "biological oxygen demand" leachates.

36 P.E. RUSHBROOK

of insufficiently "reduced" chemical conditions in the landfill to enable strictly anaerobic methane-producing bacteria to thrive and utilise the carboxylic acids produced by the acetogenic bacteria.

The continued existence of acetogenic decomposition in a landfill generally indicates a need to improve the covering of wastes to seal them from the atmosphere.

Phase IlL Anaerobic, rising methanogenic decomposition

As oxygen depletion continues and the redox potential (Eh) of interstitial waters drops to below approximately- 200 mV, then conditions become suitable for methanogenic activity to develop. Over the period of a few weeks methane concentrations begin to rise and carboxylic acids decline. This is due to the acetic acid in the leachates being utilised by the methanogens to produce methane, carbon dioxide and water. The environmental impact of these conditions is substantially less than in Phases I and II, if the site is properly engineered. Also landfill temperatures usually become stabilised in the me- sophilic range (i.e. up to 40°C). The methane generated must be properly managed to avoid off-site migration, but good landfill design can achieve this.

Phase IV. Anaerobic, stable methanogenic decomposition

This phase represents the most stable period in the decomposition of waste in controlled landfills. It is believed to persist for at least 15 to 20 years in temperate climatic areas and is characterised by methane and carbon dioxide concentrations of around 65 and 35%, respectively. Lower carboxylic acid concentrations in leachates are observed and there is a gradual depletion of the available organic carbon substrate in the waste.

Phase K. Rising aerobic gaseous composition

No-one has yet studied waste decomposition in a landfill to completion. However, evidence from very old sites suggests that once the available organic carbon is used up the methanogenic microbial activity diminishes and methane and carbon dioxide concentrations gradually decline. At some future point, it has been argued, oxygen levels will begin to rise. Eventually the remaining waste would be regarded as biologically "inert" and atmospheric gaseous conditions may become re-established. This situation has not been demonstrated in the field.

CO-DISPOSAL OF INDUSTRIAL AND MUNICIPAL WASTES 3 7

CONTROLLED LANDFILL

Good landfill does not occur of its own accord. It requires sensible design, good site engineering, orderly waste emplacement, effective gas and leachate control, and thoughtful restoration once completed. If landfill is given low organisational priority, low funding and a low calibre of staff in a municipality then controlled landfilling will not be achieved. There have seen several publications describing the development and operation of modern controlled landfills (for example see ref. [ 2 ] ) and it is not possible to discuss these in detail in this paper.

However, all landfill operations require careful planning before the first tonne of waste is received. This can be formally set out in a "working" plan. A plan consists of two aspects: ( 1 ) drawings and text detailing the development of each phase of the landfill;

and (2) a description of how site operations will be conducted.

The various types of information that go into a good working plan are listed in Table 1. Naturally, conditions will change over the lifetime of a site so a working plan has to be flexible. The philosophy behind modern landfilling in the U.K. is "progressive restoration" whereby waste is deposited into pre- constructed bunded areas, hydrogeologically separated from the rest of the

TABLE1

Elements of a landfill working plan [2]

( 1 ) Site location plan

(2) Site survey

(3)Ground investigation

(4) Site operational plan

( 5 ) Engineering plan

(6) Restoration plan

Delimit the exact boundaries of site on a suitable scale of topographical map.

Ground survey showing the existing ground levels, contours, existing drainage and watercourses, unstable ground, shafts, etc.

Review of available geological information, borehole and trial pit data.

Drawing (s) showing the layout of the site after preparation including: gates and boundaries, access to site, reception facilities (office, maintenance bay, wheelwasher, weighbridge), storage and tanks, on-site access roads, phases of waste filling, emergency waste tipping area, source of local cover material, location of bunds and site liners, new drainage pattern, leachate and gas management facilities, reception facilities for industrial wastes, and boundary landscaping.

Specialist plans detailing specific site engineering works, e.g. bund construction, leachate treatment plant, site access improvements, etc.

Drawing(s) showing the intended design and final contours of the completed landfill including: phases of restoration; final contours al- lowing for expected settlement; final drainage layout; cross-section of the site; details of the final cover to cap the site; and possible end uses and vegetation to be planted.

38 P.E. RUSHBROOK

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CO-DISPOSAL OF INDUSTRIAL AND MUNICIPAL WASTES 39

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40 P.E. RUSHBROOK

site. Each bund is typically 2 to 3 m high and is constructed in advance of waste filling. These bunded "cells" each will hold three to six months of waste (Fig. 2 ). As the first cell is filled, another is constructed adjacent to it and then used. A third cell is filled above the first and so on. In cross-section a "staircase" arrangement of cells is developed (Fig. 3 ) until the bunds in the first phase of the site reach their final level. That part of the site is then capped with impermeable cover material and restored. The staircase ofbunds continues to be constructed, progressively, across the site until the entire area has been raised to just above its final planned levels. Subsequent settlement and maintenance of the final cap will produce the final contours.

WATER BALANCE

The basis of good landfill operations is the control and management of the water balance within the site. Too much water entering a landfill means that the absorptive capacity of the waste could be exceeded and large quantities of leachate will be produced. Too little water, as in some arid areas, then waste degradation can be very slow and prolonged. Much of the landfill research investigations that have taken place over the past 15 years in the U.K. and North America have been directed towards understanding the influence of water on the physical, chemical and biological degradation and attenuation processes within wastes (Table 2 ). Much of the engineering in modem landfills, for example, cell bund construction and final cap design, is intended to prevent clean rainwater and surface water from mixing with the waste, and hence increasing the volume of leachate to be dealt with.

TABLE 2

Principal attenuation methods in municipal waste landfills

Physical processes adsorption, absorption filtration dilution dispersion

Chemical processes acid-base reactions oxidation, reduction precipitation, co-precipitation ion exchange complexation

Biological processes aerobic and anaerobic microbial degradation


C O - D I S P O S A L L A N D F I L L

Co-disposal is a logical extension of municipal waste landfill and it can be defined as:

"The disposal of difficult (chemical) wastes in admixture with municipal wastes so that full advantage is taken of the chemical attenuation and bio- chemical processes that operate within a landfill."

An essential pre-requisite to good co-disposal is the establishment of stable anaerobic, methanogenic conditions within the deposited municipal wastes. Without this, co-disposal cannot be undertaken in a controlled and safe manner. In principle, all of the chemical compounds listed in Table 3 go to landfill, though some are only present as trace contaminants in other waste streams. Table 3 also provides information on those waste types which are considered as potentially suitable for co-disposal, in concentrations typically produced by industrial processes.

To ensure that the environmental impact of chemical wastes remains insig- nificant it is important to maintain a balanced input of municipal and industrial wastes. Examples of the max imum loading rates quoted in the U.K. for selected chemical wastes are given in Table 4. It is stressed that these loading rates are not necessarily applicable in other countries and that each nation should determine these values on its own composit ion of municipal waste.

Research over the last two decades has found that co-disposal is an effective disposal option for a large range of industrial wastes [ 3 ]. All countries, developed and developing, are conducting co-disposal in some form or another, although many may not realise it. In some places this occurs at sites not engineered or managed to accept it in a responsible manner.

A co-disposal landfill is designed in a similar manner to a municipal waste site. At a co-disposal site municipal waste is deposited into bunded cells. Each cell has capacity for 3 to 6 months of waste input. Subsequently, specific cat- egories of chemical wastes can be deposited with the decomposing municipal waste. Chemical wastes arise in three forms: liquid, sludge and solid. Each is co-disposed separately using different emplacement techniques (Fig. 4).

Before any chemical waste is accepted it should be analysed in a site laboratory to verify its contents. No wastes should ever be deposited until this is done. The movement of these wastes from a producer to a disposal site should also be regulated to ensure that wastes are properly disposed of and not sent to inappropriate disposal facilities.

Liquid wastes are usually taken directly to their point of deposition at a co- disposal site, or discharged into sumps and tanks at a reception area. Liquid wastes are commonly discharged into interconnecting trenches excavated in mature municipal waste (i.e., 3 to 6 months old). These trenches are fenced

42 P.E. RUSHBROOK

TABLE 3

Schedule of listed substances (adapted from ref. [ 8 ] )

Waste types Reservations on suitability

Acids and alkalis Usually neutralised by pre-treatment

Antimony and antimony compounds Arsenic compounds Asbestos (all chemical forms) Barium compounds

Beryllium and beryllium compounds Biocides and phytopharmaceutical substances

Boron compounds Cadmium and cadmium compounds Copper compounds Heterocyclic organic compounds containing oxygen, nitrogen or

sulphur Hexavalent chromium compounds Hydrocarbons and their oxygen, nitrogen and sulphur compounds

Inorganic cyanides Inorganic halogen-containing compounds Inorganic sulphur-containing compounds Laboratory chemicals Lead compounds Mercury compounds Nickel and nickel compounds Organic halogen compounds, excluding inert polymeric material

Peroxides, chlorates, perchlorates and azides Pharmaceutical and veterinary compounds

Phosphorus and its compounds

Selenium and selenium compounds Silver compounds Tarry materials from refining and tar residues from distilling

Tellurium and tellurium compounds Thallium and thallium compounds Vanadium compounds Zinc compounds

Usually deposited in the sulphate form

Some less persistent production residues only

Persistent compounds excluded

Excluded in this form Persistent compounds

excluded and also some mineral oils

Some types only

PCB's and similar excluded

Excluded Less persistent com-

pounds only and no animal tissue

Elemental phosphorus should be excluded

Acid tars and sludges not advised


TABLE 4

Max imum loading rates for selected chemical wastes in the U.K. (Source: various U.K. government publications. )

Const i tuent Loading rate

Metals CI ~ 1 0 0 g t - t Cu a 100 g t - l Pb a 100 g t - As b variable Hg 4 g t -~ Cd 1 kg batteries t - t Zn a 100 g t -

Sulphuric acid 20 kg t - Hydrochloric acid 5 kg t - Phenols 2 kg t - Oils 2.5 kg t - Pesticides 20 g a.i. ~ t - t

PCB < 5 0 g t -~ Cyanide 1 g free CN t - Tannery sludges 66.6 kg t - t

aMetal in soluble form. bSee ref. [ 4 ]. Ca.i.: active ingredient.

off from the rest of the site and can be open or filled with coarse aggregate. The purpose of the trench is to provide a sufficient internal area to encourage seepage into the partially degraded municipal waste below. Liquid waste "in- jection" has also been used, particularly for odoriferous compounds, where permeable zones have been built up during landfilling. Several wells can be provided at different depths to spread the liquid waste over a larger volume of the municipal waste.

Wastes in sludge form are typically deposited in single trenches. However due to the nature of the material they can cause rapid blinding of the trench base and hence lead to inadequate dispersion into the underlying wastes. An alternative approach is to excavate trenches immediately ahead of the working face where municipal waste is being tipped. Sludge is then deposited in the trench and immediately covered beneath 2 m of municipal waste as the working face advances.

Solid chemical wastes are generally regarded as easier to handle than liq- uids and sludges. They are most commonly deposited in containers at the base of the working face and covered immediately with 2 m of municipal waste. An alternative method, often used for wastes which present special handling difficulties, is to place them into excavated pits in "mature" municipal waste and backfilled.

The safe operation of a co-disposal site relies on three principles:

4 4 P.E. RUSHBROOK

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TABLE 5

Toxic gases liberated as a result of mixing of commonly available, chemically incompatible substances [51

Examples of mixed incompatible wastes Resulting toxic gas

Inorganic Arsenical materials Any reducing agent Arsine Cyanides Mineral acids Hydrogen cyanide Hypochlorites Acids Chlorine Nitrates Sulphuric acid Nitric acid Copper, brass, many heavy metals ~, Nitrogen dioxide Nitrates Acids J and nitrous fumes

Phosphorus Caustic alkalis or reducing agents Phosphine Selenides Acids Hydrogen selenide Sulphides Acids Hydrogen sulphide

Organic a Dithiocarbamate Acids or alkalis Ethylene thiourea fungicides Dithiocarbamate Water Carbon disulphide fungicides

aRef. [ 6 ].

( 1 ) A high standard of landfill design and operation to ensure that municipal wastes are deposited in a controlled manner and that a stable anaerobic environment is established.

(2) Locally researched and approved chemical waste loading rates to ensure that the capacities for degradation and attentuation within the municipal waste are not exceeded.

(3) On-site staff with qualifications in chemistry to ensure that the storage, mixing and disposal of chemical wastes comply with relevant regulations and that the compatibility of chemicals is maintained. The latter is nec- essary to prevent adverse chemical reactions occurring.

With regard to item (3) above a co-disposal landfill operator must run the disposal operation so as to avoid the mixing of incompatible chemicals. The nature of any potential incompatibilities depends on the wastes permitted to be disposed at a co-disposal site. Various undesirable reactions can occur [ 2 ], i.e. (a) the generation of heat by chemical reaction (exothermic reaction ) which

in extreme cases may result in fires or even explosions, e.g. alkali metals, metal powders;

(b) the generation of toxic gases, e.g. arsine, hydrogen cyanide, hydrogen sulphide;

(c) the generation of flammable gases, e.g. hydrogen, acetylene; (d) the generation of other, undesirable gases such as nitrogen oxides, carbon

dioxide, sulphur dioxide, chlorine; and

46 P.E. RUSHBROOK

REACTIVITY REACTIVITY GROUP NAM tr GROUP NO,

| Acids. Miner=l. Non-oxidizin 8

2 Acids. Mine~l, Oxidizin I

3 A~l~. OvMn~

4 ~tlcuh~t$ jnd GI~. c~ls

Jddeh~. des

6 Amides

7 .:,mm~..Aliph:llc and ,~nUmllC

A.Io Cum~nds. Dbutu Compou~Fs and Hydr'a~line~

9 C:lr ~lmx IL'I

tO C:ustics

I ~ Oilhi~lrbmma It.l

13 f.scm

14 Elhe~

I$ Fluoride. In~pn~c

16 Hydro~rbuns..Ammtle

17 I~ lo le~led Orpniei

18 I~o~ya~.aces

19 Keton,~

20 ~4e~rxpaam and Other O~anlc SUl£Kk,~

21 Melsd~ Alblll and Alkaline Earlh. ~ l ~ d

22 MelIEL Other E ~ i a l & Alloys =s Po,dc ' l~ V=porr,. ur S~u~It-~

Metah. Other ~t'm~t t: l & .Idlo)'l a~ S~'~I S. RocK. l)rop~ Muldinm. e¢c.

24 .q~ell~ arid ~|elll Com~g~ln~ To'ok"

25 Nitride~

26 Nilriles

27 Ni lm Compou~s. Orphic

28 Hydro~xrbom..~11~1~11C. Ul~dllUt-.lied

29 Hydrocarbons. Alipl~llC. S=lum~ed

30 Peroxides and H y d ~ x i d ~ Orl=~ic

31 Plwnois and Cm,.~s

32 O ~ l a m o p h c ~ l e ' ~ ~o¢~olh iO~l l~ . Phol, p~dilltio41e'l

33 Sul F~,.,s. lnQ~llanl¢

3,4 Epoxides

101 Combuslila~ and Flammable Mulerml~ Misc~Ibncm~

102 E~ploslves

103 Pldym~z~b~ Compmmds

1114 O'~icl~ng AFnUt. S[=em,

lOS Reducing Altmel. Strops

106 W~m" and M ~ m ~ C ~ t u i n m I Walt.r

107 Water Re~cb',~ Subltam¢~

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Fig. 5. Chemical comparability of hazardous wastes [ 7 ].

CO-DISPOSAL OF INDUSTRIAL AND MUNICIPAL WASTES 4 7

FI~JRE 5 (continued)

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48 P.E. RUSHBROOK

(e) dissolution of toxic compounds including heavy metals, e.g. complexing agents, chelates.

Examples of the toxic gases that can be generated from the mixing of incompatible wastes are given in Table 5. Most work on chemical compatibility has been conducted in the U.S.A. and a summary of the results from an exten- sive study is reproduced in Fig. 5.

CONCLUSION

There is always a need to establish and maintain controlled municipal waste landfill in every municipality. This is fundamental to the improvement of waste management anywhere. Waste treatment and resource recovery both have important roles in an integrated waste management strategy for some municipalities and should be encouraged wherever practicable. In addition to municipal waste, the quantities and diversity of industrial wastes will rise as a country or region becomes more industrialised. Often co-disposal is the only practical disposal option that the economies of some countries can sustain. Consequently, the provision of facilities for the disposal of industrial wastes needs to be made. Co-disposal is probably the easiest and quickest method to adopt to bring about an improvement in controlled industrial waste management.

In tandem with improving landfill design and equipment, stafftraining and improvements in the professional recognition of landfill managers also need to be encouraged. Public confidence in any treatment or disposal operation handling municipal and/or industrial wastes can be developed only where professional standards and regular environmental monitoring are maintained. The international funding organisations also have a part to play in developing countries. They should promote and encourage projects not only for resource recovery, but also to upgrade municipal waste landfill sites to controlled operations and to establish demonstration co-disposal facilities.

REFERENCES

1 Rovers, F.A., Farquhar, G.J., 1973. Infiltration and landfill behaviour. ASCE J. Environm. Eng. Div., October 1973: 671-690.

2 Department of the Environment, 1986. Landfilling wastes. Waste Management Pap. No. 26, HMSO, London.

3 Department of the Environment, 1978. Co-operative programme of research on the behaviour of hazardous wastes in landfills. HMSO, London.

4 Department of the Environment, 1980. Arsenic-bearing wastes. Waste Management Pap. No. 20, HMSO, London.

5 Keen, R., 1980. Operator hazards in toxic waste disposal. Ph.D. Thesis, University of Aston, Birmingham, U.K.

6 Stevens, C., 1982. Harwell Laboratory, U.K., unpublished information.


7 Environmental Protection Agency, 1980. A method for determining the compatability of hazardous wastes. EPA 600-2-80-076, U.S.

8 HM Parliament, 1980. Control of Pollution (Special Waste) Regulations, 1980. Statutory Instrument No. 1709, HMSO, London.

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Co-disposal of industrial wastes with municipal solid wastes