cleaner production in mauritian cane-sugar factories

Journal of Cleaner Production 8 (2000) 503–510www.cleanerproduction.net

Cleaner production in Mauritian cane-sugar factories

T. RamjeawonDepartment of Civil Engineering, Faculty of Engineering, University of Mauritius, Reduit, Mauritius

Received 24 June 1999; accepted 23 March 2000

Abstract

A growing awareness of the impacts of pollution on the environment, coupled with the introduction of sectoral effluent standardsby the Mauritian environment authorities, have led to the current situation whereby the sugar factories need to introduce appropriatewater and wastewater management systems. The cane-sugar industry has been given 3 years to comply with the legislation oneffluent standards. During that 3 year period the industry will have to investigate cleaner production opportunities, select appropriatewaste treatment technologies, gain operational experience and confidence with the technology and introduce environmental manage-ment systems. The case-study taken from the cane-sugar industry in Mauritius illustrate the extent to which environmental improve-ments are possible through cleaner production. 2000 Elsevier Science Ltd. All rights reserved.

1. Introduction

The food industry is one of the world’s largest indus-trial sectors. In some countries or regions, it is the largestsingle manufacturing industrial sector. While food pro-cessing is not considered to be amongst the mostenvironmentally hazardous industries, nevertheless, theycan cause severe organic pollution if designed or oper-ated with insufficient attention to the environment. Theenvironmental problems common to all food processingsectors are [1]:

1. high water consumption, especially problematic inwater-poor or water-stressed countries

2. the generation of liquid effluent with high organiccontent

3. the generation of large quantities of sludge andsolid wastes.

To solve these and other environmental problems, thefood industry should adopt cleaner production methodscompared to traditional end-of-pipe approaches to pol-lution control. Water use can be drastically cut throughin-house recirculation systems. High organic load waste-water can be effectively treated to digest its biological

E-mail address:[email protected] (T. Ramjeawon).

0959-6526/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved.PII: S0959-6526 (00)00020-2

contents greatly reducing its polluting potential. Liquidand solid wastes can be reused.

In 1862 there were some 259 sugar factories on theisland of Mauritius, producing about 150 000 tonnes ofsugar. The number of factories has now fallen to 14,although the intensity of production has significantlyincreased such that an average of 600 000 tonnes of canesugar are produced each year. In Mauritius, sugar canecovers 40% of the island’s total area of about 2000 km2,representing about 80% of the cultivable land. The sugarcane industry employs about 20% of the labour force andcurrently accounts for around 28% of the export revenue.Despite significant expansion of the manufacturing sec-tor sugar export still represents a significant net foreignexchange earning sector due to its relatively low inputin terms of imports.

These factories are spread around the island and havetraditionally been major consumers of water, and arealso considered to be major sources of non-toxic organicpollution in surface water bodies, and subsequently inthe lagoons which receive these waters. A growingawareness throughout the industry of the impacts of thispollution on the environment, coupled with the introduc-tion of sectoral effluent standards by the Mauritianenvironment authorities, have led to the current positionwhereby the sugar factories need to introduce appropri-ate water and wastewater management systems. Thecane-sugar industry faces the challenge of significantlyincreasing its overall resource efficiency — obtaining the

504 T. Ramjeawon / Journal of Cleaner Production 8 (2000) 503–510

maximum of useful products from minimum rawmaterials and other impacts, including energy and water.The case-study taken from the cane-sugar industry inMauritius illustrates the extent to which environmentalimprovements are possible through cleaner production.

2. Use of process water

2.1. The process

Water supply is required for the following processes:

O during extraction, as imbibition fluid to remove thejuice from the fibre, and as cooling water for themachinery used to extract the juice;

O during evaporation, as feed-water to the barometriccondenser (or as make-up water, where condenserwater is re-circulated);

O during crystallisation, as cooling water for the tanksof massecuite; and

O during power generation, as cooling water for theturbo-alternators used to generate electricity (fromburning bagasse), as make-up water to feed theboilers, and as feed-water to the furnace flue-gasscrubbers (or as make-up water, where scrubber wateris re-circulated)

O miscellaneous usage such as cooling waters forpumps, factory washings and milk of lime prep-aration.

The following section presents the typical water con-sumption figures for each of these processes, and for thesugar processing industry as a whole in Mauritius.

2.2. Quantities used

It has been estimated that during the 1991 milling sea-son the sugar factories in Mauritius abstracted about 45million m3 of water for processing [2]; an amount com-parable with the annual domestic water consumption ofthe island. This water is abstracted in accordance withthe Rivers and Canals Act of 1863, which grants riparianlandowners the right to take an amount of water for irri-gation commensurate with the crop area and the avail-able flow, free of charge.

Table 1 shows the typical water use for six selectedfactories in Mauritius. It is clear from this table that,whilst the factories are not net consumers of water, theiroverall usage varies considerably. This is mainly due to:

O availability of water to the factory;O whether or not barometric condenser water is recycled

(factories A, B and D do not); andO the efficiency of water management policy within

the factory.

Table 1Water-use at selected Mauritian sugar factories [3]a

CaneWater input Wastewater

Factory throughput(m3/tc) (m3/tc)

(TCH)

A 65 12.6 12.8B 95 7.7 8.0C 101 2.3 2.6D 112 6.1 6.9E 124 2.1 2.5F 240 1.8 2.7

a Notes: difference between input and output is attributed to moist-ure extracted from the cane. TCH, tonnes cane per hour; m3/tc, cubicmetres per tonne of cane.

Table 2 shows the detailed water consumption at twofurther factories. It is evident from the table that the mostwater-intensive operations at these factories are conden-sation of the vapour during evaporation, and scrubbingof the flue gases during bagasse combustion. However,the water use during these operations is considerablyreduced when re-circulation is practised, as is demon-strated by factories C, E and F in Table 1.

Whilst a considerable amount of data have been col-lected regarding water-use in the various Mauritian sugarfactories, raw water intake is only monitored on a regularbasis at seven factories. This is in part due to the waterrights law which allows fairly unrestricted access to sup-plies. However, many factories are coming around to theview that with any right there is an obligation, and thatthey have a responsibility to use water efficiently inorder to conserve supplies for the island. Mauritius hasalready reached a water-stress situation which requiresserious attention otherwise water availability can presentto be a limiting factor to social and economic develop-ment. Further industrialisation, the growing tourist

Table 2Breakdown of water inputs to selected factories [3]a

Process stream Flow rate (m3/tc)

Factory G Factory H

Imbibition water 0.22 0.30Cooling water:

turbo-alternators 0.10 0.10milling tandem 0.36 0.41crystallisers 0.14 0.15

Boiler make-up 0.15 0.11Scrubber feed 1.00a 1.30a

Scrubber make-up 0.03 0.14Condenser feed 0.00 1.06Condenser make-up 6.88b 11.28Total 8.88 14.85

a Partial re-circulation of scrubber water.b Partial re-circulation of condenser cooling water.

505T. Ramjeawon / Journal of Cleaner Production 8 (2000) 503–510

Table 3Volumes and pollutant loads for wastewater at selected factories [3]a

Volume [1] BOD5 CODFactory TSS (kg/tc)

(m3/tc) (kg/tc) (kg/tc)

A 12.8 – – 2.20B 8.0 0.51 0.98 0.38C 2.6 0.69 2.79 1.59D 6.9 0.61 1.39 0.23E 2.5 0.42 0.74 0.24F 2.7 0.53 0.94 0.67

a BOD5, biological oxygen demand (5 day incubation); tc, tonne ofcane; COD, chemical oxygen demand; TSS, total suspended solids.

industry, the increasing need for irrigation water toimprove yield and growth in water requirement for dom-estic purposes will all lead to increasing demand forwater from sources traditionally used solely by thesugar industry.

3. Waste streams

The total pollutant loads in the process wastewaterstreams for the six factories discussed previously areshown in Table 3. Loadings have been shown withrespect to tonnage of cane processed, since this producesa more meaningful comparison between factories thatdischarge varying amounts of wastewater than wouldaveraged pollutant concentrations. It is evident that theBOD5 loading is relatively constant between factories,but that COD and TSS vary considerably, mainly due tothe relative efficiency of the fly-ash removal systems atthe factories.

Table 4 shows a breakdown of the wastewater streamfor factory “C”. The table shows that the main sourceof organic pollution is the cooling waters and floor wash,which contains a high concentration of dissolved sugarfrom plant spillages. Thermal pollution is introduced by

Table 4Pollutant loadings in wastewater streams from factory “C” [3]a

Temp.Stream Volume BOD5 COD TSS Oil pH

(°C)

m3/tc m3/day mg/l kg/day mg/l kg/day mg/l kg/day mg/l kg/day

Cooling waters and0.3 660 1820 1201 3400 2224 344 224 23 15 6.2 27

washingsExcess condensates 0.3 660 380 251 630 416 5 3 – – 7.6 72Boiler blowdown 0.2 55 130 7 300 17 65 4 – – 10.1 81Scrubber overflow 0.1 220 100 22 1210 266 1480 326 – – 8.5 42Spray-pond

1.7 3740 60 224 110 411 55 206 – – 7.1 40overflowTotal 2.6 5335 1705 3334 763 15

a BOD5, biological oxygen demand (5 day incubation); COD, chemical oxygen demand; TSS, total suspended solids.

the excess condensates and boiler blowdown streams,whilst the fly-ash scrubber overflow contains a high con-centration of suspended solids. Of particular note fromthe table is the fact that the cooling waters and floorwashings contain 70% of the organic pollutant load,whilst only constituting some 12% of the wastewatervolume.

The most polluting discharges from the factories areactually generated outside of production times, at week-end washdowns (generally Sundays) and end-of-cropshutdown washings. During these periods, the variousequipment are scrubbed and hosed down, creating largevolumes of waste effluent which have extremely highsugar enttrainment and suspended solid concentrations.The average BOD5 during weekend washdowns is over4000 mg/l, and at the end-of-crop washdown reachesover 20 000 mg/l when the crystallisation tanks arestripped and cleaned.

Table 5 shows the Environment Protection (EffluentLimitations Standards for the Sugar Industry) Regu-lations 1996, which were published very recently by theMauritian Ministry of Environment. World Bank guide-

Table 5Sugar factory effluent standards

World BankParameter Mauritian standard[4] guideline

standard[7]

Condenser Other factorywastewater wastewater

pH 6.0–9.0 6.0–9.0 6.0–9.0Temperature (°C) 40 40 ,3°C increaseChemical oxygen

50+Ia 100 150–250demand (mg/l)Total suspended

30 60 50solids (mg/l)Oil (mg/l) 5 5 10

a Refers to influent raw water.


line standards for the sugar manufacturing sector havealso been presented in the table for comparison purposes.The majority of sugar processing plant effluents exceedthese threshold limits, with the possible exception of thepH standard. As discussed in the earlier section, the rela-tively low level of wastewater treatment at the majorityof the plants is such that the effluent which reaches thesurface watercourses does not generally conform to thestandards in the table.

The impact of these pollution levels on downstreamsurface water users (such as locals bathing or washingtheir clothes) generally consists of a disruption to theiractivity and the frequent occurrence of obnoxious odoursin the vicinity of the watercourse. This is particularly thecase during weekend and end-of-season plant wash-downs, when decomposing organic material is mostprevalent in the water.

In conclusion, the sugar processing plants wouldappear to have a significant impact on the water qualityin those watercourses which receive their effluents.

4. Options for water conservation in cane sugarfactories

In addition to wastewater treatment, another effectivemeans of reducing pollution from wastewater effluentsis to reduce their volume by carrying out water conser-vation measures within the factory. Additional benefitsfrom such approaches are a reduction in water usage,with the commensurate benefits to water resources avail-ability on the island. Investigation of the water cycle insugar factories shows that for proper operation the fac-tory requires around 12C tonnes of water at all timeswhere C is the tonnage of cane crushed. This impliesthat if no water recycling is practised then the factorywould require an input of 12C tonnes and would dis-charge at least the same amount (excluding water presentin fresh sugar cane). Based on experience acquired dur-ing this study it can be concluded that the water require-ment can be reduced to 1.5C with partial recycling. Afew sugar factories in Mauritius have already reducedtheir water requirement to about 2C. A number of suchmeasures are possible within the cane sugar process,primarily based upon the principle of recycling effluentprocess waters. Additional benefits from suchapproaches are a reduction in water usage, with the com-mensurate benefits to water resources availability on theisland. This could result in a significant reduction inannual freshwater requirement for sugar manufacturefrom 45 to 10 million m3. A water flow model of a 100TCH factory practicing partial recycling is presented inFig. 1. The water consumption of the factory is 2.2 m3

per tonne of cane. Sugar cane contributes 0.7 m3

water/tonne and 1.5 m3 water/tonne of cane must be pro-vided from external sources. A fraction of the incoming

water is lost to the atmosphere by evaporation andanother fraction in various by-products. Consequently,the wastewater from the cane sugar factory is around 1.5m3 per tonne and of which 40% is condensate water.

The following sections present a number of optionsfor water conservation in sugar factories. Many of thesepractices are already in place in one or more of the Mau-ritian factories, although no one factory employs all ofthem. Obviously, the overall benefits to the environmentwill vary from option to option; a comparison of theirbenefits is therefore given in the last section.

4.1. Spray pond to recycle barometric cooling waters(option A)

As shown earlier in Table 2, barometric condenserwaters represent the largest water usage in the sugar fac-tories. These waters can be recycled by introducing coo-ling towers or spray ponds which maintain the tempera-ture differential between the inlet and outlet of thecondenser.

Accounting for evaporation and wind drift, it is esti-mated that approx. 8.32 m3 of water per tonne of cane(m3/tc) could be saved by introducing a spray pond at a150 TCH factory, at a capital cost of approx. $0.5M andan annual operating cost of $50 000 [5].

4.2. Treatment and recycling of flue gas scrubbingwater (option B)

Effluent from the fly-ash scrubbers can be filtered andre-used as feed-water to the scrubbers. The resulting fly-ash sediment can then be dried and used as soil condi-tioner or stocked and disposed of at the end of the sea-son.

Accounting for evaporation and the water content ofthe leftover fly-ash, it is estimated that approximately0.79 m3/tc could be saved by recycling the scrubberwater at a 150 TCH factory, at a capital cost of approx.$200 000, and an annual operating cost of $15 000 [5].

4.3. Recycling of excess condensates (option C)

With the exception of the early stage evaporates inthe refinement process, which are recycled as boiler feedwater, later stage condensates are generally dischargedas wastewater due to their high level of sugarentrainment. However, these condensates could berecycled as imbibition water, scrubber water, makeupwater in the barometric spray pond and for other miscel-laneous purposes such as floor washing.

It is estimated that approx. 0.64 m3/tc could be savedby recycling the excess condensates at a 150 TCH fac-tory, at a capital cost of approx. $75 000 (for hot waterstorage, pumping etc.), and an annual operating cost of$5000 [5].


Fig. 1. Water flow model — factory capacity 100 TCH (all figures represent water flow in Tonne or m3/h).

4.4. Recycling of turbo-machinery cooling waters(option D)

The installation of a small package cooling tower (ofabout 100 m/h capacity) would enable the recycling ofthe plant machinery cooling water. In addition, since thebearing cooling water generally picks up oil and grease,a separator would also be needed in the process.

It is estimated that approx. 0.63 m3/tc could be savedby recyling the machinery cooling water at a 150 TCHfactory, at a capital cost of approx. $100 000, and anannual operating cost of $20 000 [5].

4.5. Treatment and recycling of factory wastewaters(option E)

The water used for cleaning the factory during week-days and at weekend shutdowns constitutes the main pol-lutant load to the environment. This water could betreated, for instance using the UASB process asdescribed later and recycled as make-up water to thebarometric condenser and/or fly-ash scrubber, factorywashing or irrigation.

It is estimated that approx. 0.4 m3/tc could be saved by

recycling the treated factory wastewaters at a 150 TCHfactory, at a capital cost of approx. $160 000, and anannual operating cost of $45 000 [5].

4.6. Summary

Table 6 summarises the water savings and costs asso-ciated with the water conservation options described inthe previous sections. It is clear from the table that byfar the largest amount of water saving occurs from

Table 6Summary of water conservation options for sugar factories [5]

Operation andWater saving Capital cost

Optiona maintenance(m3/tc) ($US)

($US)

A 8.32 500 000 50 000B 0.79 200 000 15 000C 0.64 75 000 5000D 0.63 100 000 20 000E 0.40 160 000 45 000Total 10.78 1 035 000 135 000

a Options as described in preceding sections.


recycling the barometric condenser water. As mentionedpreviously, due to relative water scarcity in the north ofthe island, this is already practised at several Mauritianfactories. Although this constitutes the largest water sav-ing, the biggest impact on pollution control is made bytreating the most concentrated pollutant streams: the fly-ash scrubber outflow and the factory floor washings.Whilst treatment of the fly-ash scrubber water alreadytakes place at almost all of the factories, very few effec-tively treat the factory floor washings. For this reasonfrom an environmental point of view, options B and Efrom the table are strongly recommended for introduc-tion industry-wide in Mauritius, whether the resultanttreated effluent is recycled or simply discharged to theenvironment.

5. Pollution control

5.1. Existing wastewater treatment technologies

There are two particular liquid effluent streams fromsugar processing plants which are potentially highly pol-luting and require treatment:

O fly-ash slurry from the flue gas scrubbers in thebagasse incineration plant, herein referred to asslurry; and

O wastewater from the weekend and end-of-seasonwashings, and other miscellaneous sources, e.g.machinery cooling waters, herein referred to aswaste-water.

With the exception of fly-ash removal systems, currentwastewater treatment facilities in Mauritian factorieswhere they exist are generally inadequate, largelybecause of overloading and poor maintenance. Inaddition, there is a fundamental problem with the treat-ment systems used at present, in that the multiple anaer-obic lagoon system, whilst relatively cheap and effectivefrom a technological point of view, requires a relativelylarge land area — a prohibitive factor on a small islandstate such as Mauritius. There is, therefore, a need toconsider alternative options for wastewater treatment atthe sugar factories. This is discussed further in the fol-lowing sections.

5.2. Cleaner production opportunities

Prior to considering options for treating factory waste-waters, efforts should be made to minimise the volumeand pollutant concentration of the effluents to be treated.Options for water conservation has been discussed in theprevious section; pollutant concentrations can bereduced at source by the following methods:

O good housekeeping including reducing spillages andmopping them up with bagasse, ducting leakagesfrom vessels and recycling them back into the pro-cess, and maintaining machinery to reduce oil andgrease leaks;

O oil and grease removal, using on-site traps to facilitatethe recycling of plant cooling waters (discussed later);

O improving the efficiency of the entrainment separatorsin the vacuum evaporators to reduce the carry-overof sugar droplets into the barometric condenserwater; and

O temporarily storing excess juices and liquids fromtanks and heaters during periods of weekend wash-down, and returning them to the process after clean-ing.

It is strongly recommended that some or all of thesemeasures are carried out at all factories in addition to(and in advance of) the installation of any wastewatertreatment facilities. Other measures which should also beconsidered are the reprocessing of high sucrose contentwastewaters at the end-of-crop washdown, and thereduction in frequency of plant washdowns, for instanceto once every two weeks. The latter would effectivelyhalve the volume of the most polluted waste stream fromthe factory. Carrying out such measures in advance ofthe installation of treatment technology will reduce thepollutant loading on the treatment system and may evenenable a reduction in the specification of the equipment.

As shown earlier in Table 4, there are several liquidwaste streams from the plants which have varying pol-lutant makeup’s and concentrations. It has been determ-ined that the most efficient to treat these wastewaters forre-use or disposal is to separate them into three mainstreams:

O fly-ash scrubber and spray pond overflows;O condensates and boiler blow-down water; andO machinery cooling waters and floor washings

(including weekend washdowns).

Table 7 shows the resulting pollutant characteristics fora typical model 150 TCH factory. It is apparent fromthe table that the first, and possibly the second (if sugarentrainment is reduced as discussed earlier) of the wastestreams would only need to be discharged to lagoons forcooling and slight anaerobic digestion before they couldbe discharged to the environment or re-used: therebyconsiderably reducing the scale and expense of treat-ment. The last of the three streams, however, wouldrequire significant treatment before disposal. It shouldbe noted that the aggregation of the wastewater into threestreams would require three separate drainage systemswithin the factory, which may prove difficult in oldestablished factories where alterations may be difficult.


Table 7Pollutant loadings in combined wastewater streams from a model 150 TCH factory [3]a

Volume BOD5 COD TSSStream

(m3/day)

mg/l kg/day mg/l kg/day mg/l kg/day

Cooling waters and washings 990 1820 1802 3400 3366 340 337Condensates and boiler blowdown 1073 361 387 606 650 10 11Scrubber and spray-pond overflow 5940 62 368 171 1016 134 796

a BOD5, biological oxygen demand (5 day incubation); COD, chemical oxygen demand; TSS, total suspended solids.

5.3. Options for treating factory wastewaters

The four most appropriate methods for treating themost polluted wastewater (i.e. the cooling and washingwaters) from sugar processing plants, which can be usedin isolation or in combination, are:

O waste stabilisation ponds;O aerated lagoons;O extended aeration; andO upward anaerobic sludge blanket (UASB).

Table 8 presents a comparison of the performance (andestimated costs) of these most appropriate options fortreating the sugar factory wastewaters, for a typical 150TCH sugar factory. The methods relate to combinationsof the aforementioned techniques, as follows:

O anaerobic lagoon followed by facultative pond (i.e.“natural” lagooning);

O anaerobic lagoon followed by aerated lagoon;O anaerobic lagoon followed by extended aeration; andO UASB plant followed by sedimentation tank.

It is apparent from the table that the UASB option rep-resents probably the most appropriate solution for thetreatment of Mauritian sugar factory wastewaters. Inaddition to the relatively efficient performance indicatedin the table, advantages include the following:

Table 8Comparison of performance (technical and financial) of 150 TCH sugar factory wastewater treatment options

Annual operationalBOD5 removal Power required Capital investment

Method Land required (ha) costsa (% capitalefficiency (kWh) [6] ($US @ 1991)

investment)

Anaerobic lagoon followed by facultive70–80% 3.80 0 120 000 ,0.1%

lagoonAnaerobic lagoon followed by aerated

80–95% 0.55 26.5 200 000 0.3%lagoonAnaerobic lagoon followed by extended

75–85% 0.60 29.0 625 000 2.0%aerationUASB followed by sedimentation tank 85–90% ,0.1 Energy recovery 180 000 ,0.1% [3]

a Figures are based on 150 TCH throughout, 1550 m3/day wastewater volume, 4500 kg/day COD loading and 3000 BOD5 kg/day loading.

O the investment and operating costs, when the cost ofland is taken into account, are likely to be amongstthe lowest of the four options;

O the ratio between the annual financial burden of was-tewater treatment and the annual turnover of a 150TCH factory (approx. $27.6M) is,1%;

O the technology is relatively simple (although stafftraining would be required for its operation); and

O the reactor can be built to almost any scale, therebyenabling it to form part of a decentralised wastewatertreatment system (i.e. at each factory).

6. Conclusion and recommendations

Whilst water is not in extensive supply on Mauritius,at present there are no serious conflicts of use betweenthe sugar factories and the island as a whole. Therefore,it is not recommended that expensive water conservationmeasures are introduced per se at the moment, but thatselected measures are introduced in tandem with thewater pollution control measures. That is, where it isrecommended that wastewater streams are treated then,where possible, the treated effluent should be recycledor used for irrigation rather than discharged to theenvironment. As a consequence, the level (and hencecost) of treatment may be lessened where the qualitystandards for recycled water are less onerous than thosefor discharges to the environment (as discussed in thenext section).


Although it is not recommended that water conser-vation measures are introduced industry-wide, it isrecognised that many factories already employ suchmeasures where their supply is constrained. This is prim-arily in the drier north of the island. It is therefore thecase that the overall incentive for the introduction ofwater conservation measures will vary between factories.

The following strategy is recommended for the intro-duction of wastewater treatment facilities at sugar factor-ies in Mauritius.

O The factory wastewater should be separated into twoor three streams, most importantly separating the mostpolluted wastewater (factory washings and machinecooling water) from the large volume of relativelyunpolluted barometric condenser water, therebyreducing the scale and expense of treatment required.

O Treatment facilities should be installed for the mostpolluted wastewater streams:— the factory washings and machine cooling watersshould be treated in the most cost–effective andefficient manner — studies to date would appear tosuggest that the UASB process (followed by second-ary sedimentation) would be the most appropriateoption— the fly-ash slurry from the flue gas scrubbersshould be treated either by screening/clarification orby filtration/sedimentation ponds (most factoriesalready have such equipment, although given thepresent pollution problems, it needs to be routinelyserviced and maintained to improve itsperformance).

O Full consideration should be given to the staged intro-duction of the above technologies, for instance byintroducing sedimentation ponds prior to the fullUASB systems (which could subsequently work inseries when both are in place). This could be com-bined with monitoring of the ambient quality in thereceiving waters such that the need for further stagesof treatment is determined prior to the expenditurebeing made. In addition, the possibility of combinedtreatment systems for groups of factories should beconsidered to introduced economies of scale and ther-eby reduce the financial burden on individual factor-ies.

O Alternative end-uses for the treated water (rather thandisposal to watercourses) should be considered, e.g.recycling as process water or irrigation supply. In thisway it may be possible to reduce the requirement fortreatment (and hence treatment costs) where therequired quality standards for the recycled water areless onerous than those for environmental discharges.Nevertheless, it is likely that some of the wastewaterwill still need to be discharged to the environment,particularly during wet periods: in such cases it would

be sensible to reserve the full treatment process (e.g.UASB with secondary sedimentation) for the portionof the wastewater which is to be discharged to theenvironment, and only partially treat the re-usedwater.

O Finally, if a continued programme of water qualitymonitoring in the receiving waters demonstrated theneed, treatment systems should be introduced for theless polluting wastewater streams (e.g. the barometriccondenser spray-pond overflow). It is likely that thesewastewaters could be simply discharged to lagoonsfor cooling and slight anaerobic digestion before theycould be released to the environment or re-used (NBclearly if water conservation is a priority issue at afactory, for instance in the drier northern area, thentreatment and recycling of all significant wastewaterstreams should be considered it not already practised).

The above strategy represents a phased introduction ofwastewater treatment facilities in Mauritian sugar factor-ies. Whilst it is important for the sugar industry to meetthe standards set by the environment authorities at theearliest possible opportunity, given the obvious impor-tance of the industry to the socio-economic welfare ofMauritius, it is essential that there is a degree of flexi-bility on the part of the authorities with regard toenforcement. In this respect, it is recommended thatdetailed programmes are developed for the introductionof appropriate pollution control technology, to includeclearly defined targets and timescales, agreed betweenthe authorities and the industry, towards achieving com-pliance with quality standards in the medium to longterm. An essential component of these programmeswould be a programme of water quality monitoring todetermine the effectiveness of the measures taken, andthe requirement (if any) for the introduction of sub-sequent phases.

References

[1] UNEP. Food processing and the environment. Industry andEnvironment 1995;18(1):3.

[2] Baguant J, Ramjeawon T. Water management in Mauritius. Inter-national Sugar Journal 1996;98(1171).

[3] Ramjeawon T. Integrated management of cane-sugar factory was-tewaters in Mauritius using the Upflow Anaerobic Sludge Blanket(UASB) process. PhD thesis, University of Mauritius, 1995.

[4] MOEQL. National environmental standards. Ministry of Environ-ment and Quality of Life, Port Louis, Mauritius, 1997.

[5] ERM. Preliminary environmental assessment: cane sugar pro-duction in Mauritius. Environmental Resources Management.Final Report, 1996.

[6] Chaux D. Pollution prevention and abatement guidelines for canesugar processing and refining. UNIDO, Project US/GLO/9, 1993.

[7] World Bank. Pollution prevention and abatement handbook. Sugarmanufacturing. Washington, DC: The World Bank, 1997.

cleaner production in mauritian cane-sugar factories

Documents