Published on 03/01/2018
Reducing Pollution Load on ETP. Saving costs. Some suggestions for Sugar Mills.
By Dr. Yashpal Singh
- Cane Yard unloading and carrier section
Cane trash, cut pieces, cow dung and other solid wastes are generated at the Cane yard unloading and the carrier section. They have a potential of adding to suspended solids and creating odours, apart from the run off from these areas either existing a pressure on the water bodies or adding to the pollution load on the S.T.P.
- Cane trash, cut pieces, cow dung and other solid wastes from the cane yard should be regularly collected, and segregated at the cane yard. The biodegradable should be used in composting and the not easily biodegradable sent to land fills.
- Solid wastes from cane yard should not be allowed to meet the drains.
- Drains should be kept covered to prevent bagasse from the carrier section flowing into drains.
- Continuous and regular accumulation of cut cane pieces below the cane carrier will add to the liquid pollution.
- Milling section
Spills and leakages from mill house operations like gland cooling, floor washings and bearing lubrication may contain oil and grease and high organic loads. In addition, spillage of bagasse and bagacillo materials, spillage of cane juice from rollers, screens and while pumping the diluted juice for recirculation, leakages of juice from gutters, whirling tanks, overflow of juice from whirling tanks and the washing of mills with hot waters may create additional pollution loads. It is advisable to:
- Collect oil and grease in trays. Store in drums and sell as low grade lubricants or burn in boilers after mixing with bagasse.
- Give proper slope to shop floors and adopt dry cleaning. Keep the soiled wipes away from drains. Dispose with other solid wastes.
- Use mechanical seals for all pump glands and alarms for overflows. Collect leakages and spillages in a pit and recycle into the process.
- Collect desuperheater and mill bearing cooling water and recycle back into the process.
- Avoid excess application of lubricants.
- Properly guide, bearing cooling waters back into troughs or funnels without allowing the same to flow out and create effluents.
- Avoid spillage of bagasse and juice by properly guiding the delivery pipelines of juices.
- The spurting and spilling of juices from rollers must be avoided by suitable guide plates.
- Closely monitor fugitive discharges and emissions and plug leakages in time.
- Regularly renew gland packings.
- Bagasse Handling
Storage handling and movement of Bagasse through Conveyors may give rise to dust particles, suspended solids, air pollutants and fibers which may also add to the organic load of waste water by reaching the drains. It is suggested that
- The Bagasse in the Bagasse storage yard could be cleaned and collected at the end of the crushing season and used for composting.
- A closed transfer system should be put in place.
- Drains should be covered so that the bagasse does not enter into drains.
- Arrest fugitive bagasse dust generated at bagasse transfer points.
- Clean the screens used to collect bagasse on the conveyor regularly.
- Clean bagasse dust accumulated at the bottom of the blowers.
- Boiler House and Boiler Section
- The quality of Boiler Blow down can be improved by proper maintenance and checking feed water quality.
- Too much of excess air pressurising the furnace and over loading the boiler should be avoided in order to minimize the escape of fly ash.
- Boiler ash should not be allowed to accumulate and it must be removed as and when produced and disposed as authorized.
- Clarification, Evaporation and rotary filters
Periodical washings, overflows, spillages, leakages from pumps, glands and pipes overflow may lead to additional effluents. The following measures could also be taken-
- Regular maintenance and monitoring to arrest the pollution due to pump leakage.
- Provide metallic packaging in case of perpetually leaking pumps like clear juice, vapour cell juice pumps etc.
- Level indicator, limit switches, overflow alarms and automatic level controllers could be provided to avoid overflows.
- Leakage collection pits could be provided near each cluster of pumps. The liquid thus collected should be pumped back to the process source.
- The leaked materials should in no way find their way to drains.
- Any accidental spills as leakages may be contained in a reasonable area using bagasse and the bagasse so used must be transferred to the mills or on to the bagasse conveyor depending on the juice content in such bagasse.
- Separate storage tanks should be provided for collecting the day washings from the periodical cleaning of heating surfaces in evaporator vessels and juice heaters. This should be allowed to be mixed with normal effluents slowly and steadily to avoid sudden surges of temperature and chemical constitution in the feed to the ETP.
- All gland cooling waters from the pumps should be collected separately for reuse for imbibitions purposes.
- Filter cake, filter mud or press mud generated at the filter press should be stored and handled so as to avoid spillage in all circumstances. It should not be allowed to mix with any wash water/rain water.
- Entrainment from Pans and Evaporator-
Poor operating conditions, pump leakages and entrainment of sugar through vapours from Pan boiling and evaporation may result in condensate which may adversely affect the quality of effluents. It is suggested that
- Additional external catches could be provided for the last body of evaporators and all vacuum pans.
- Poly baffle stainless steel could be used instead of umbrella type save alls.
- Pump glands to be provided with mechanical seals to prevent leakage.
- The catch all in evaporator and pans should be checked frequently for any choking of the pipes/holes meant for draining back the collected liquid.
- High load of juice in the evaporators should be avoided.
- Vacuum fluctuations should be avoided.
- Sampling ports could be provided on the vapour pipes of all the pans and the last body of evaporators. Regular tests must be made for finding out any sugar getting entrained with the vapours.
- Washing and cleaning of Juice Heaters and pan evaporators
Washings from scale removal and cleaning result in high inorganic content waste waters. In order to minimise generation of these effluents and resultant shock loads to the E.T.P. it is suggested that :
- NaOH/Lime could be recycled for the next cleaning.
- The effluents could be stored in a leak proof holding tank with overflow alarms to avoid shock loads on E.T.P.
- Laboratory effluents could be segregated and connected to the storage tank.
- Alternative cleaning methods without chemicals could be explored. Cleaning of scales by electric driven flexible shafts using compressed air could be tried.
- Partial softening the scales before high pressure cleaning could also be tried.
- Aisles could be kept clear of obstructions.
- A spill prevention and management plan could be put in place and all spills documented.
- Sulphur and Lime Houses
- Washings of sulphur and lime houses generate inorganic waste waters containing carbonates and sulphates. These should also be collected separately and fed in a regulated way to the ETP in order to prevent shock loadings.
- Molasses storage tanks
Poor storage, handling and transport of molasses has a very great impact on the quality of effluents to the ETP. It exerts a very high Biological oxygen and chemical oxygen demand. Molasses spillages and unwanted accumulation create problems. It is suggested that
- Handling of molasses should be careful without spillages at transfer points and in transportation on roads.
- Garland drains and Collecting pits should be provided around the tanks for storage and transfer of molasses.
- Overflow alarms, inlet valves, washout valves, outlet valves, outlet for pumps, temperature gauges, manhole vents should be fitted to molasses storage tanks as prescribed.
- Lids and vents should be provided on tanks.
- Floors should be immediately cleaned of spillages, using dry cleaning or other appropriate cleaning system.
- Regular lifting of molasses should be monitored
- Closed transportation and conveyance system should be preferred for Molasses handling.