Document 5bjLgYVe4B3n324nkV9b23n45

Chemistry and Industry, 18 April 1981 271 particularly for small-to-medium sized works in rural areas, the expectation is ti)at sludge disposal to land will continue, albeit perhaps in a mhdified form. This continuation is conditional upon the containment of potential problems associated with micro-pollutants. Sludging has increased the amount oluertain heavy metals to levels greater than the original naturarb^ckground concentration. Whether or not these increases areSienificant in terms of contaminating food chains is less certaihvMore research is required, full consultation is essential and Ihqits must have regard for the economic implications as well at the risks. Only in this way will realistic limits emerge whibh while protecting the environment, do not unnecessarily penalise either those responsible for disposing df sludge or theft, customers. Acknowledgements. While this paper is published with the permission of the Director of Planning, the views expressed are those of the author and not necessarily of Thames Water. References 1 DoE/NWC Standing Committee on Sludge Disposal's Survey 1975 2 Coker, E. G,, `The utilisation of liquid digested sludge', in `Papers and proceedings of the WRC Conference on Utilisation of Sewage Sludge on Land, 1979' 3 Hewitt, E. & Smith, F. V. P., Plant Mineral Sntrittan, 1975 4 Pike, E. B., &. Carrington, E. C., 'The effects of conventional sludge treatment processes on pathogens', in 'Papers and proceedings of the WRC Conferen:.* on Utilisation of Sewage Sludge on Land, 1979' 5 Thompson, L. H.. & Dickens, W. J., "The land utilisation of sludger from urban works', `Papers and proceedings of the WRC Conference on Utilisation of Sewage Sludge on Land, 1979" 6 Wood, L. B., King. R. P., & Norris. P. E. E., `Some investigations into sludge amended soils and associated crops and the implications for trade effluent control", in `Papers and proceedings of the WRC Conference on Utilisation of Sewage Sludge on Land, 1979' 7 Abson, J. W., 'Detoxification of sewage sludge', Institution of Chemical Engineers Conference on Practical Solid Waste Disposal, 1980 8 Lindsay, D. G,, `Possible health hazards from the presence of persistent chemical residues in sewage sludge', in `Papers and proceedings of the WRC Conference on Utilisation of Sewage Sludge on Land, 1979' ''6 Chumley, G. C-, `Maximum permissible levels of metals in sewage aludge applied to land', ADAS Advisory Paper No. 10, London. MUFF, 1971 10 Beaten, P. H. T., Davis, R. D., &. Brindley, P., "The disposal of sewage sludge onto farmland: the scope of the problem on toxic elements', A>//irf. Conte^l, 1979 11 DoE NWC Report of the Working PartyGqn the Disposal of Sewage Sludge td>Land, Tech. Rpt. No. 5,1977 12 Jamieson, D. G., `TbewMential for using sewage sludge as livestock feed', in `Pap^htand proceedings of Institution of Chemical Engineers Conference on Protein and Livestock Feed from Biological Waste Water Treatment Plants, 1976' Amounts and effects of toxic materials discharged to sewers Robin Chalmers An *sses$RKDt of the effects of toxic materials discharged to sewers 2 complicated by the fact that the toxicity of materials -juries not only according to the nature and con centrations of the materials themselves, but also according to the nature of the receiving environment. Sewers may discharge to treatment works or directly to surface waters or the sea. Manufacturing operations vary with the nature of the product made, the size of the manufacturing operation, the degree of application of good practice in minimising dis charges and the extent of water recycle or re-use adopted. The amounts of wastes then discharged to sewers is further influenced by the extent of pre-treatment prior to discharge, which is dictated by the standards required for those effluents, which vary from location to location. In practice however, the amount of toxic materials ac tually discharged by an industry, is determined in most countries by the limits prescribed by the sewerage authori ties. These limits are derived either from an approach of using the `best available technology economically achievable' for elimination of pollutants by pre-treatment of the wastes (the USA's aim for 1983) or from an assessment of the amounts of a substance which can be accepted into sewers Mr Chalmers is a consulting chemist and chairman of International Consulting and Laboratory Services Birmingham. He is also senior consultant of its Bo stock Hi!f and Rigby Div'sion. 288 Wiodso' STrf- ' Birmini'r.ir', p" '. ~i ` without damage to a sewage treatment system or to the ultimate receiving environment. This approach, based upon environmental quality objectives, is the one currently adopted in the UK and some other European countries. Ft is therefore the effects of toxic materials which should, and generally does, determine their amounts in discharges to sewers, and examples of these are given later. According to recent WHO estimates (1979) about 60,000 chemicals are frequently used in daily life, and this number increases at the rate of some 200 to 1000 new chemicals per year. Knowledge of their toxicity, particularly chronic toxicity, is not always complete and limits have to be framed with some factor of safety. Some interplay exists between what is achievable and what is desirable in limiting discharges to sewers. It is therefore important to know how wastes arise and how effectively they can be minimised at their points of origin. Limits can then be determined more or less realistically and where this is desirable, as in some developing countries, introduced in phased stages. For this reason, some attention is given to the amounts of wastes, and their variability, as they arise. What is toxic 7 Toxicity may be defined as the ability of a chemical molecule or substance to produce injury once it reaches a susceptible site in or on an organiM-n. The word i* derived from the Creek. Toxikntt poison for jrr-'Ws. ToviciU is a clieiiiic.ti ph,r . r ' n. I ! , k , .. i . . 11.. i ' i y f-1, | . " . , I . ` (' r\>- . .inc li.uu; . 1c -V'1 '.961 URL 03693 Toxicity maj also he selectixc, even though the laws of genetics apply almost universally. A practically universal biochemistry of mitosis can be inferred from evidence that toxic agents such as colchicine arrest the process of mitosis at one particular stage in all species.1 However, despite the common basis for living matter there are marked biochemical differences between the various species and in the bio chemistry of various tissues within any one species. Selective weed killers and pharmacological agents are well known. The question of what is toxic must therefore be examined carefully. Not only does the toxicity of a substance vary with the nature of the chemical itself and of the substrate upon which it acts, but also with its concentration, e.g. common salt may be toxic in some circumstances. It is there fore a matter of degree as well as of kind, and it is important that when considering `toxic" wastes, one should also bear in mind the nature and volume of the waste in relation to the receiving environment. This bears upon the acceptability of the wastes for discharge to sewers, pre-treatment requirements if any, and the standard required, which should be relevant and scientifically based.2 The position is complicated further by the tremendous difference in the response of test organisms towards toxic substances, depending upon temperature, aeration, hardness of water, age and condition of the test organism, and the conditions under which the test is carried out. There may be a thousand-fold difference in the toxic concentration of the same substance quoted by different authors.3 Apart from direct toxic effects, trade effluent discharges may be objectionable for other reasons. The phrase `Poison ous. noxious or polluting" recurs in the UK water pollution control legislation, although its definition is left to the courts. For the present purpose, toxic substances are taken to include those which impair or inhibit treatment processes. Variability in trade effluent discharges Souses of trade effluent discharges should be critically examined because action at this stage can significantly red&e toxic effects and simplify subsequent treatment Variations in the quality of trade effluents at the sources may be classified into: 0 Cyclic variations Discharges from electro-plating and similar cyclical pro cesses; Discharges of phosphating and body pre-treatment from automobile manufacturers; Brewery and largescale food manufacture discharges, with a regular production cycle. 0 Seasonal v ariations Discharges from food processing, canning and freezing which vary with crops available and fish caught. 0 Variations associated with discharge of strong spent `dumping' solutions Aircraft engine manufacture, with strong discharges con tained for pre-treatment; Automobile manufacture with strong discharges metered into running swills flows. 0 Variations due to irregular process changes Random variations in multiple products produced at organic dye works; Variations in production by herbicide munufac- Tuhlc ) Wali-r demand of some major industries Industry ______ Water demand t ejljnd Cars, at a? pj.(nts ICJ Biliingham Brii'vh S'eet Cr>rpo^;nion The Ccr. v> t Luiricity Generating 2 x tO-'nr1 each week 2 x 10-'m? each day 2 x 10-rm' each half-hour 2 x I0'iv.: coch minute Bhaid ' v't-.m- oulpul lurers. due to market requirements; Variations in tannery operations. 0 Variations resulting from modifications to production processes in pollution control programmes The elimination of dumping strong solutions b> in-plant treatment; Alterations to the nature of the solutions in use by elimination of. e.g. cyanides from some plating operations or introduction of *Jow-cyanide` processes; The introduction of re-use and re-cycle procedures. Examples of the extent of such variations, which have been met in a busy consulting practice, have been published elsewhere.4 Discharges from large-scale automatic electro plating showed fluctuations where none were expected, and indicated pre-treatment design parameters. Variations in brewery discharges showed the gain possible from balancing the strongest discharge flows and of programming discharges for night-time or slack periods. Variability in industrial water requirements Table 1 compares, on atime baas, the water demand of some major industries.5,6 Of more practical interest is the use of water per production unit as shown in Table 2. The large variation of water consumption is significant; lower water usage is an indication of good management and better pro duction control and is usually accompanied by a lower wastage of the product. The South African figure of 5m-Vt of steel is one of the lowest in the world,7 and much can be learnt from a study of good practice in such hot developed countries where water is scarce. Amounts of wastes from manufacturing operations Amounts of wastes vary according to manufacturing opera tions. In the Netherlands pollution coefficients are ascribed to a large number of industrial wastes, based upon a popu lation-equivalent (pe): 1 pe -- grams COD -+ 4.57 gramsN - 180 The coefficients vary from 0.5 per employee for textile spin ning and weaving to 20 for chemicals manufacture. In a very broad classification of industrial effluents. UK authorities listed:8 0 Effluents from food and drink manufacture; 0 Other organic effluents, including those from paper, leather and wool industries; 0 Effluents containing metals and cyanides; 0 Chemical effluents. Effluents in the final two categories are potentially toxic,9 and some data can be derived from examination of production sources. Metal finishing wastes Approximate annual consumptions of chemicals by the UK metal-finishing industry in 1973 were listed by Mattock.10 The losses to effluent ware assessed as 10-20 per cent of the cadmium, copper, tin and zinc consumed; 50 per cent of the nickel, and 70 per tent of the chromic acid; and virtually 100 per cent of the cyanides. Toxic organic chemicals A number of valuable development documents for effluent limitations guidelines have been produced for the US Em ironmental Protection Agency (EPA). That for the `significant organic products '-cement' of organic chemical manufacturing.1' includes extensive tables of nianif ..luring  Chemistry and Industry, 18 April 1981 Table 2 Order of magnitude of outer consumptions associated with different industries Industry Water intake per unit Brewing Dairies Electroplating, galvanising Fruit processing Motor cars Paper making Potato processing Poultry processing Power generation Slaughter houses Rolling mills Steel Sugar beet Tanning Textile processing Yeast manufacture 8- 25mVt 1- |3m3/t 10- SOlitrcs'm2 surface 4- 7m3,'t 10*100m3/car S-260m3/t 15- 65m3/t 30- 35tn3/IOOO chickens 3-100!ttres/kWh 1- 20m3/cattle unit 2- I6m3/t 4-300mJ/t 5- 20m*/t 74- 88m/t 80-600m'/t 90-ISOnWt process raw waste loads from which the list in Table 3 has been abstracted. The sections correspond to: # Continuous vapour phase processes where contact pro cess water is used as diluent, quench or vent gas absorbent; 0 Continuous aqueous liquid-phase reaction systems; 0 Batch and semi-continuous processes. There is a large variation in flows, loading, and concen trations. The BOD and COD concentrations shown are based on wastewaters coming directly from the process, and do not necessarily represent the waste concentrations which a typical single-state biological waste treatment plant would accept. In most cares the concentrated wastewater would be diluted with less concentrated wastes from other processes or with slightly contaminated waters. The best available technology economically achievable, (BATEA, 1983 Stan dard) is based on the addition of activated carbon treatment, following biological treatment. Polychlorinated biphenyls The PCBsfcrm a classic case of a refractory organic substance that resist^degradation in the environment by all means. They shoURl not occur in discharges to sewers. In the USA the EPA has banned all manufacturing discharges of PCBs, but care is still required in the disposal of surviving PCB sources - principally in dielectric insulating and cooling fluids in capacitors and transformers. In the mid-1970s the waste load of PCBs discharged to waterways or sewers in the USA was assessed as less than 5kg/d - principally from the capacitor industries. Much greater quantities were discharged to land or in scrap oils to incineration - those from the capacitor industries were estimated to be 2000 and 18Q0kg/d respectively. 273 Pesticides There are more than 500 individual pesticides of commercial importance, and as many as 34,000 distinct major formulated products.12 In a major study13 the EPA classified the waste loads from the three principal types of pesticides produced as shown in Table 4. This Table illustrates clearly that the wastes produced by an industry may be substantially reduced by pre-treatment before discharge to sewers or disposal by other routes. Amounts discharged to sewers In addition to variations inherent in the manufacturing pro cesses and the extent to which good practice is adopted in minimising the discharges, pre-treatment will often sub stantially reduce the amounts of wastes involved. The extent of pre-treatment applied is determined either by quality conditions imposed by regulatory agencies or by the economic advantages in pre-treating to minimise acceptance charges. The weights of toxic substances which may be discharged to sewers is therefore substantially determined by what the receiving sewage disposal works, if any, can receive and treat or dispose of satisfactorily. In developed countries, and many developing countries, concentrations which deter mine these amounts are prescribed by law. In Great Britain, approximately half of the flow of sewage received at treatment works in 1970 was composed of in dustrial effluent.9 This amounts to 6.8 x I06m3/d of industrial effluent, but the figure has been dropping significantly in the past 10 years. In addition, a considerable flow of industrial effluent is discharged directly to water courses or to the sea, either with or without prior treatment. This is summarised in Table 5,54 which shows discharges for England and Wales. An investigation in Venice15 showed the major significance of discharges from the chemical and allied industries Approximately 50 per cent of the discharge flows (135,000m3,d) and 75 per cent of the organic load from the industrial complex of 239 factories at Porto Marghera was associated with chemical and allied manufacturing. The weights of toxic materials discharged in such flows may be approximately derived from the consent conditions applied for their reception into sewers. In the UK where consent limits apply, the average concentrations of a toxicant discharged in a pre-treated effluent is about two thirds of the limit. It is well known that a sewage treatment works designed to produce an effluent with BOD and SS not exceeding 20 and 30mg,'litre respectively is likely to give an effluent having values about two thirds of these figures on average.2 The same is broadly true of trade effluent pre-treatment plants, which in my experience are designed on this basis. The validity of Table 2 Organic chemicals protection: process raw waste loads Product Product description Flow (litre/0 Benzoic acid and benzaldehyde Chlorobenzene Chiorotoluene Maleic anhydride Acrylonitrile Cresol, synthetic Propylene glycol Sec-butyl alcohol D>c and dve intermediates Miscellaneous batch chemicals Pi^sti..: ,,'r, Catalytic oxidation of toluene Chlorination of benzene Chlorination of toluene Oxidation of benzene 2840 50 121,000 2300 Ammoxidation of propylene Methylation of phenol Hydrolysis of propy lene oxide Sulfonation and hydrolysis of mixed butylenes 4470 334 5500 626 Batch manufacture < s.-'t.*n I'f !*(- h *' -I'M'.\il i.lc 947.000 78.\Kt 6?U Process raw waste loads BOD COD (mg.litre) (mg'litre) 9010 300 2 47,000 17,900 7700 15 126.000 8620 143,000 3 22,800 32.800 303.0tX) 10 62 000 620 12^1' 30h psu I?' ' > URL 03694 >! :;4 C! . r j-.;-, i; -.Ij-v ,. It i; l URL 03695 this approximation is illustrated by the results at a major UK sewage treatment works which receives 635kg/d of total toxic metals in allow of 385M)itres/d. From the consent limit of 30mg/litre total toxic metals, the expected daily load would be 578kg although there is some contribution from domestic and storm water. Limits for other toxic chemicals are prescribed individually where necessary, if not already limited by a general restriction on the COD. Determination of these limits requires con sideration of the acute and chronic toxicity of the substance at the most critical point in the circumstances prevailing. This may be in the sewers, storm overflows, biological treat ment, sewage sludge, or the effluent ultimately discharged and requires a detailed knowledge of the characteristics of the substance including, for example, its biodegradability as shown in Table 6. Limit figures for toxic non-metallic substances in in dustrial effluent discharges tend to be misleading, since they depend significantly upon the local conditions. In the UK there are general prohibitions on the discharge to sewers of petroleum spirit, calcium carbide, and effluents at a higher -temperature than 43.3C. Limits for these are effectively zero, and limits for substances in the `black list' of the EEC are tending to zero. In deriving loads from consent limits, care is necessary to use the actual volumes discharged to sewers rather than the permitted maximum volumes which are generally higher. It should be remembered too that industrial water consumption is no longer rising at the 3 per cent per annum compound rate that was forecast 10 years ago. It has been estimated in the UK that a 10 per cent increase in production is likely to be accompanied by only a 5 per cent increase in water consumption. Weights of materials discharged to sewers are also tending to fall significantly with the application of advanced technology. Effects of discharges to sewers Ther^are some advantages in discharging chemical and other mdu^Erial wastes to sewers for treatment at sewage disposal works. They often show increased amenability to bio oxidation when treated in combination with sewage, and the domestic sewage stream can supply the necessary nutrients often lacking in industrial wastewaters. In addition, the Table 4 Waste loads from pesticide manufacture Halogenafed organic pesticide plant Production (small plant), t/d Production (large plant), t/d Flow litre/t Total pesticide kg/t Total pesticide mg litre After treatment by BPT, mg'litre 16.2 85.7 35,000 0.327 9.26 0.09 Organophosphorus pesticide plant Production (small plant), t/d Production (large plant), t/d Flow litre/t Total pesticide kg't Total pesticide mg'litre Aficr treatment by BPT, mg'litre 6.57 72.0 43,900 0.454 10.34 0.04 Organonitrogen pesticide plant Pu'du.iion (small plant), id Production flaige plant), l/d Flow Jitre/t Total pesticide kg t Total pesticide mg litre After ft'dimem by BPT. me litre 9.4? 116 35,400 2.82 79.66 0.20 BPT ReM practicable technology Table 5 Discharges of industrial effluents in England and Wales industrial effluents to sea (10'mVd) Electricity generating stations (mainly cooling water) Chemical and allied industries Iron and steel industry Food processing and manufacture 1.3 0.04 0.04 21.6 20 Gas and coke production Paper and board manufacture All others 0.03 0.02 0.17 1.6 (More than 50 per cent of the 1.6 x 10*ms/d of significant dis charges is through private outfalls independent of public sewers) Industrial effluents to inland rivers under water authority control (!0*m-/d) J 0.8 dilution of chemical wastes afforded by the domestic sewage can reduce the concentration of potential inhibitory or toxic chemicals to a level harmless to the treatment or ganisms, thus enabling waste to be effectively degraded. However, many chemical an^allied works produce large volumes of effluent of high strength, compared with sewage, and local sewage treatment works are often insufficiently large to deal with either the organic or the volume load.16 In addition, if chemical wastes are accepted into the local sewers, stringent safeguards are essentia] to prevent effects Upon the fabric of sewers, men working in the sewers, and efficient operation of sewage works. A classification of toxic materials used and toxic wastes produced in different in dustries is given by Toogood and Hobson.17 Volatile toxic substances In order to comply with the UK Health and Safety at Work Act 1974, sewerage authorities must control discharges to sewers of any material which may be toxic or injurious to their employees. The UK Water Research Centre produced an excellent report in June 1980 on the determination of safe limits for the discharge of volatile materials to sewers.17 This gives a scientific basis for the derivation of limits for ammonia, sulphur dioxide, hydrogen cyanide, hydrogen sulphide, and 50 volatile organic substances which max reach sewers at low concentrations in industrial effluents. Consideration is required of the threshold limit value (TLV) in an atmosphere in equilibrium with sewage, vapour pres sure, limiting activity coefficients, temperature, and in the case of inorganic substances, pH value. Indicated limits for sewage flowing in a sewer include: 4.lTng/litre and 0.09mg/ litre for hydrogen cyanide and hydrogen sulphide respectively at pH 7.0 and 15C; 1.7mg/litre and 1.2mg/litre for xylene and trichloroethylene respectively at 25C. Other factors affecting the toxicity of atmospheres in sewers which may need to be considered include the relative atmospheric toxicity of a mixture of volatile toxic substances, and the effects of ventilation in sewers. Many other volatile organic substances are under investigation. Where data are not available for any suspect substance they should be determined experimentally: methods have been indicated by the Water Research Centre and by Thames Water Authority. The indicated limit for hydrogen sulphide is well below the concentration of about lmg'litre usually found in domestic sewage, although ventilation in most sewers is likely 10 render thal figure safe. There is little if any room however, for the acceptance of sulphides in industrial effluent dis charge^ Tltic is of significance to a number of industries Chemistry and Industry, 18 April 1981 275 ' notably tanneries and gas works. Sulphides, or conditions for their formation from sulphates, are also restricted in sewers to minimise corrosion effects. In an investigation by my colleagues in Baghdad, contributory factors to severe sewer corrosion by sulphides were found to include dis charges of sulphates from battery manufacture and dis tillery wastes in addition to septic sewage. Sewer flows of 0.8-1.0m/s tend to prevent the formation of sulphide in sewers, and this criterion is sometimes used in design in connection with corrosion prevention. However, in the light of current knowledge, the potential toxic effects of sulphides are usually the dominating constraints. Toxic products formed in sewers The discharge of substances that may interact with others present in sewers to form toxic products is normally re stricted under UK legislation. While many such reactions can be predicted, others are less obvious and it is necessary to remain alert for these. In investigating a death in a sewer atmosphere I found that highly volatile and toxic dichloroacetylene had been formed from the interaction of trichlorethylene and sodium hydroxide - an effect previously associated mainly with die reaction of soda lime [and trilene in closed circuit anaesthesia in child birth. Aqueous poisons Concentrations of poisons which are acceptable in sewage flows or storm overflows because they are not toxic to sewage treatment processes do not pose significant hazards to people working in sewers. Substances which may attack the sewers, or cause fires or explosions are restricted for these reasons. Effects on sewage treatment Many, if not most, chemical works produce large volumes of effluent of high strength compared with sewage. BOD loads in ckccjs of 50,000mg/litre are not uncommon in cer tain waste steams. While these are toxic in the concentra tions produced, dilution at a large sewage treatment works such as Davyhulme, Manchester allows effective treatment of the substantial chemical waste flows there.' In other cases pre-treatment of the waste prior to discharge to sewers may be mandatory. Thus, a synthetic fibre factory producing 27m3/d of effluent at 15,000mg/litre BOD and discharging to a relatively small sewage treatment works, had to apply extensive pre-treatment including bio-oxidation in com bination with domestic sewage from the site. Toxicity Aerobic sewage treatment processes are affected by many toxic metals in the range < 1--lOmg/Htre. Table 7 shows acceptable concentrations for typical processes. Most or ganic substances exert such effects only at higher concentra tions, and cyanides have been successfully treated at con centrations well in excess of 1 Omg/litre. Metal concentrations in industrial effluents may therefore have to be controlled so that the sewage does not contain more than the limiting amount that will affect the most sensitive part of the sewage treatment process. This applies tq metals in solution. Metals in suspension, apart from some tendency to dissolution in sewage, are removed on sedimen tation treatment, and these accumulate in the sludge to gether with those from secondary sedimentation after re- i'ii hiM; ,1 iiciTMKiU Ri of nu-r.i' .hoinj Table 6 Degree of removal of various chemical wastes by biological oxidation Compounds reduced 0-10 per cent Ammonia Acetophenone Ethylene cyanohydrin Compounds reduced 70-90 per cent Acetaldehyde Acetic acid Acrylonitrile Butanol Compounds reduced 10-30 per cent Acetone Methyl ethyl pyridine Compounds reduced 30-54 per cent Ethylbutanol 2-Ethylhexanol Ethanol Hexanol iso-Propanol iso-Propyl ether Naphthalene Styrene Toluene Methanol Paraldehyde Compounds reduced 90-100 per cent Benzene Compounds reduced 50-70 per cent Acrylic and butyric acids Dioctylphthalate Phenyl methyl carbinol Benzoic acid Crotonaldchyde Ethyl acetate Ethyl acrylate Ethyl benzene 2-Ethylbexy! acrylate Heptane activated sludge treatment varies with the influent concen trations. Although figures approaching 100 per cent re moval have been reported from Ontario, these are unusual and associated with low influent concentrations. More typical are those found at Dallas, USA18 shown in Table 8. The distinction between the effects of metals in solution and in suspension leads to the possibility of differential limits for their amounts in trade effluent discharges to sewers and some authorities apply these. It is, however, the total amount accumulating in sludge which nowadays is often the dominating constraint on the reception of metals into sewage treatment. Biodegradability A significant number of organic compounds are not sus ceptible to biological degradation, or are affected only to a limited extent. Some indication of these has been given in Table 6. In such cases, their effects on passage through a sewage treatment works must be assessed from a knowledge of their toxicity in relation to the receiving environment, and this is an arithmetic exercise. Passage of toxicants The fate of chemicals on sewage treatment is not always known, and may have to be determined experimentally. It is important to establish if they are completely removed on sewage treatment and what amounts accumulate in the sludge; whether there is any release to atmosphere during sewage treatment processes (including heat treatment of sludge where this is applied); and what amounts of the original substances or toxic degradation products may appear in the final effluent discharge. In an investigation of the treatment of herbicide effluents, the removal on experimental pilot trickling fitters was 72 per cent. Increasing the herbicide content of the sewage from 0.4 per cent to 0.8 per cent caused a 16.4 per cent deterioration in treatment efficiency. There was some ac cumulation of herbicide in the sludge, which has impli cations for its ultimate disposal. Effects on sewage treatment works design The presence of toxic or high-load chemicals in industrial discharges to sewers influences the nature as well as the size of the sewage treatment works required Recent investigationin S'* ria h:i\ e shmi r> th.ri ih - n;o>y ! >'I I1- . o- i i try tt in '' URL 03696 p * 276 C1 *. .>* r .jrK' l iOwj'.fy. i r process at two works being designed has been effectively determined by the 30 per cent or so of industrial wastes to be discharged to sewers. Effects on sludge treatment and disposal Anaerobic processes of sludge digestion are particularly susceptible to toxicants and it may be necessary to limit the amounts of individual toxic metals in the sewage flow to <2mg/litre, chlorinated hydrocarbons to <lmg/!itre and anionic detergents to <30mg/litre. The presence of toxic chemicals in a sludge may determine whether or not it is acceptable for disposal to agricultural land or to the sea. Pesticides and herbicides are significant in this connection. Of even greater effect however, are metals which in many countries are limited for disposal to land by legal constraints or guidelines. Dumping to sea is strictly controlled by the Ministry of Agriculture, Fisheries and Food in the UK and by many European countries following the conventions adopted in Oslo, London and Paris. Effects upon receiving waters River quality objectives are being established for many rivers and these vary with the downstream use of the water. The World Health Organization limits for drinking supplies form the basis for many of the standards applied to po tential drinking sources. Limits applicable to fish of various kinds, together with synergistic effects of poisons and the mineral water quality are also reasonably well established for many substances, Where information is lacking on acute toxicity, fish toxicity tests form a useful guide, and a water which is non-toxic to fish is often regarded as safe. There are however, a number of cases where little or nothing is known about the chronic toxicity of organic chemicals and in the absence of adequate information these are often prohibited. Health effects Whilj much is known about the effects of many chemicals in conujon use - the Russians have standards for more than 500 chemicals in drinking water supplies - there remain many for which the effects, particularly chronic effects, are .not yet known. Increased analytical capability in recent years has shown the presence of large numbers of micropollutants in river waters. Following a case of ground water pollution in Vicenza Province in Italy, the WHO Regional Office foT Europe convened a working group on criteria and guidelines foT halogenated aromatic compounds in Venice in September 1979. The group's report covers the major uses and environmen tal occurrence of the substances, and their physical, chemical and toxicological properties, and assesses the health hazards. It recommended, inter alia, systematic environmental im pact assessments before decisions are made regarding the Table 7 Typical acceptable metal concentrations Heavy metal ion Acceptable concentration for aerobic processes of sew age treatment (mg/Iiirc) Oxidation of Nitrification organic compounds of ammonia Cd Co crtvn Ph Ni Ag 7n J 25 1-5 10 2.5-10 0 03 3-25 5 1 1-10 - 1-2 ) Table B R i-mova! of metals: Dallas tertian, plant Metal Plant influent (mg/Jitre) Removal by activated sludge (per cent) Cd 0.0)3 39 Cr 0.215 57 Cu 0.092 33 Hg 0.00051 69 Ni 0.073 21 Pb 0.095 56 Zfl 0.320 65 siting and design of chemical plants, and the establishment of safeguards in the prevention of occupational risks and the control of liquid and gaseous emissions and solid wastes. Data from the International Register of Potentially Toxic Chemicals was also considered to be of use. Effects on manufacturing costs This developing knowledge imposes significant costs upon industry, which is generally responsible and responsive. Minimising, or eliminating discharges of specific substances to sewers has a bearing-on the siting and development of new factories and imposes cosfron process modifications, pre-treatment requirements and extensions to sewage treatment works. The effects can be substantial, e.g. the adoption of best practicable technology for treatment of wastes from pesticide production involves the costly addition of activated carbon treatment to existing systems. Weiss20 in 1978 studied the cost to the USA zinc industry of complying with environ mental regulations and judged the impact on future develop ment. He determined that compliance with regulations could increase the cost of zinc by about 10 per cent and that some high-cost producers might have to shut down. During the past 10 years, nine smelters in the United States have closed, w ith the costs for environmental control being a major factor in several cases. Generally however, industry accepts these costs, so long as they are shown to be necessary, and collaborates with research and development organisations concerned with the water cycle. It is in countries where water is scarce, such as South Africa, where this shows most dearly. There, industry is collaborating with the Water Research Commission in a comprehensive investigation on the effect of potentially harmful chemicals in effluents, with a view to determining policies that should be followed in connection with water re-use. C r3Do vJ References 1 Albert, *SeJective loxicity', London. Me/hun, 1951,11 2 Jenkins, S. H., & Chalmers.>R. K., *Sumdards; making them fit the facts', Water Pofhrt. Control, 1973,72 3 `Water quality criieria', (eds. J. E. McKee & H. W. Wolf) JiaoQnieMo California Stare Water Control Boaid, Publication No. 3-A, 1963 4 Chalmers. R. K., `Manufacturing operation* and effi- L-nt quality'. Prog. )i ate/ Techno!., Iy76, 8, 329-46 5 Ar>der>on. D., The economic implications of watei re-use'. Paper presented at Cooling Water Association Symposium, 21 April 1976 6 Line* G. `Com industry of using water', Paper presenrej to the f.'fluent and Water Treatment Cr-tv-intion. London. 1PM 7 Han. O . A H,n/cn. M. R , `F ac'c- affecting the rc-use of jic: Chemistry and Industry, 18 April 1981 in industry', prog. Water TechnoL, 1975, 7, 905 8 Ministry of Housing and Local Government, 'Taken for granted', London HMSO, 1969, 38 9 Ministry of Housing and Local Government, 'Standards of efflueot to rivers with particular reference to industrial effluents', London: HMSO, 1968 10 Mattock, G., `Developing patterns of effluent treatment and recovery practices in the metal finishing industry'. Paper presented to SCI international conference, Amsterdam, May 1974 11 `Development document for effluent limitation guidelines for the significant organic products segment of organic chemical manufacturing', USA: EPA, November, 1975, 440/1-75/045 12 Hackman, E., & Ellsworth, Toxic organic chemicals - destruction and waste treatment', Hew Jersey: Noyes Data 1978, 148 13 `Development document for effluent limitations guidelines for pesticide chemicals manufacturing*, USA: EPA, November, 1976. 440/l-75/060d 14 Agg. A. R., 'Marine pollution and marine waste disposal'. Prog. Wattr Technol. Supplement, 1975, 75 277 15 Chalmers. R. K., & Jenkins, S- H., `A feasibility study of the control of pollution from industrial waste waters discharged into the lagoon of Venice', Water Pollut, Control, 1976, 75, 176 16 Reynolds, L. F., `The disposal of waste water from the chemical industry'. Proceedings or 3rd PHE Conference, Loughborough University, January, 1970. 65 17 Toogood, S. J., 5c Hobson, J. A., The determination of safe limits for the discharge of volatile materials to sewers', Stevenage: Water Research Centre, June 1980, Technical Report TR 142 18 Nriagu, J. O., `Copper in the environment, Part ). Ecological cycling'. Hew York: Wiley 1979, 128 19 `Toxicological appraisal of halogenated aromatic compounds following groundwater pollution*. Report on a WHO Working Group, Copenhagen: WHO Regional Office for Europe, 1980 20 Weiss, M., The impact of environmental control expenditures on the US copper, lead and zinc mining and smelting industry'. Report, National Economic Research Associates, Inc., Hew York. 1978 URL 03698 Treatment before discharge John M Sidwick and fcjchard Barnard Many manufacturing processes the toxic chemicals, often in solution, If not dealt with by\he manufacturer these chemicals, or their derivatives, find their way into the trade effluent streams discharging from theVindustrial premises. The trade effluents pass directly or irairectly to surface water or, less often, to ground water. In\order to protect the environment, or treatment facilities such as municipal sewage treatment works, the concentrations\and/or loads of any toxic constituents have to be reduced tot acceptable levels. The question of acceptable levels for specifidvchemicals is complex, and other factors must be considered. These include the possible presence of toxic materials from, other sources, the qfcture of the receiving environment ana. the uses to whiclrit is put, the interaction between one toxic constituent and others that may be present, and the currer state of knowledge about toxicity. Trade effluent survey If it is required that the toxicity of the effluent be lessened, and if the requirement is reasonable, the toxic constituents must be reduced in concentration, removed altogether, or converted to a less toxic or non-toxic form. Whichever approach is most appropriate and economical will cost money and final decisions should not be taken lightly; they must be based on a thorough understanding of the characteristics of the waste in question, and how it arises. The first step therefore, should be a comprehensive examination of all the waste-related manufacturing processes including flow measurement, sampling and analysis at selected points within the factory as well as at the points of discharge of effluent. As a result of a careful and expert interpretation of the data resulting from a properly designed study, decisions can be made. The main stages of activity available to the designer are shown in Fig 1. Mr Sidwick is an associate of Watson Hawksley, Terriers House, Amersham Road, High Wycombe, Bucks, and a director of Environmental Resources Ltd Mr Barnard is a chemist in the Process Dtsis" G-o'.jf o( War on Hn.-.t';'.-- . \ Table / Some common pollutants'- their origins and treatment methods Type of waste and \ Possible treatment Pollutant some sources methods Acids Any mineral or organic acid causing pH depression to < 6 usually requires treatment. Typically: Battery manufacture Steel industry Chemical works Neutralisation using alkali - typicatly lime or sodium hydroxide. Alkalis Presence of any alkali causing pH to rise to >9 usually requires ' treatment. Typically: Laundries Textile industry Chemical works Neutralisation using acid - usually a mineral acid such as sulphuric or hydrochloric. Usually free ammonia (ammoniacal nitrogen) but combined nitrogen can create problems. Typically: Coke oven effluents Domestic sewage Fertiliser factories Desorption by air stripping. Nitrification possibly followed by denitrification. Incineration. Chemical oxidation. Biodegradable waste Organic wastes with no toxic compounds presentsNutrients may hava to be added Typically'' Domestic seNyage Food waste Settlement if necessary. Biological treatment followed by settlement and tertiary treatment if necessary. Chromium Chromium often present in hexavalent form Which is most toxic. This is\ soluble as chromate add dichromate. \ Typically: ' Plating wastes Chrome tanning AJuminii.rii anodivm.' Boiler vs.iicr hlo-^Jown Cr** reduced to Cr5' by electrolysis or Chemical reduction prior to removal by coagulation and settlement. Can be removed dircctls by \ii>n-CNchai;;'C Direct -vi1 h h.i: ...ii. . '-.l ito R. .i . s s OD STATE PLANNING OFFICE EO. Box 44426 Baton Rouge, Louisiana 70804 o `i > s.