Journal of Cleaner Production 11 (2003) 327–331 www.cleanerproduction.net Water savings and sludge minimization in a beet-sugar factory through re-design of the wastewater treatment facility Filiz B. Dilek ∗, Ulku Yetis, Celal F. Go¨kc¸ay Department of Environmental Engineering, Middle East Technical University, 06531 Ankara, Turkey Received 14 August 2001; accepted 14 March 2002 Abstract The task of rehabilitating the already existing waste treatment facilities of a sugar factory was undertaken. A detailed survey of the water and wastewater streams indicated a necessity for immediate action towards water conservation within the plant. The spent waters from the beet-washing unit were first being intercepted at an integrated solids–liquid separation system (ISLSS) where they were partially recycled for reuse. Sludge from the ISLSS was going to an end-of-pipe treatment plant composed of lagoons. In order to conserve and recycle water, it was firstly deemed essential to modify the operating regime of the ISLSS. Consequently the sludge going to the lagoons could be decreased by one third. Next, the existing lagoons were re-arranged to comply with the discharge standards, at a very little extra cost. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Beet sugar effluents; Rehabilitation; Slurry treatment; Waste management; Water recycling 1. Introduction sumption of 54 000 m3. Although the factory practised reuse of flume waters following a primary treatment, the In a beet-sugar plant numerous sources of wastewaters recycle was only about 89% at every pass. The remain- exist. Among these are the flume waters that are used ing 11% of the flume waters were reaching a lagoon for washing beets soaked with dirt. These waters are also system that was acting as a means of end-of-pipe treat- used as a means of conveying beets between processes. ment, established away from the factory. The process wastewater originates from the flushing of The integrated solids–liquid separation system exhausted cossettes from the diffusion battery cells and (ISLSS) was basically designed for recycling and reus- then the partial dewatering of the exhausted pulp. The ing the flume waters. The system was composed of five so-called Steffen waste results from the extraction of sequential units: a top (root) remover, a grit chamber, sugar from molasses by the Steffen Process. The flume a pulp separator, a circular settling basin and a set of water represents about 70% of the total waste volume. rectangular settling basins operating in series, as shown The organic load of this stream is comparatively low, in Fig. 1. The top remover serves for filtering and whereas process wastewaters are high in organics con- removal of beet tops or roots from flume waters. The tent, as well as the Steffen waste. These make up only tops and pulps removed (520 m3/day and 40 m3/day, a small fraction of the total waste volume [1]. respectively) are then sold to farmers to be used as ani- mal feed. The grit collected (100 m3/day), is hauled to 1.1. Amasya sugar factory water recycling practice a nearby site for land disposal. Effluents leaving the pulp remover pass to the settling basins for the removal of The capacity of the Amasya beet-sugar factory is 6000 fine sand particles. The settled overflow is then recycled tonnes of beet per day, with a daily flume water con- to be used for washing and for moving sugar beets around the processes. ∗ Corresponding author. Tel.: +90-312-210-5877; fax: +90-312- The ISLSU also receives other wastewater streams 210-1260. originating from the sugar production line, such as coo- E-mail address: [email protected] (F.B. Dilek). ling waters, cleaning waters, pulp-press waters, etc. 0959-6526/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S0959-6526(02)00029-X 328 F.B. Dilek et al. / Journal of Cleaner Production 11 (2003) 327–331 1, along with the relevant discharge standards. From this table it is evident that the effluents were unfit either for direct discharge or for crop irrigation in their existing states. Hence, the objective of the present work was set to recycle as much water as possible within the sugar production processes and to lower the final effluents cost-effectively to the level of discharge standards, so as to dispose of these safely to the receiving waters or use them for irrigation. Therefore, rehabilitation of the exist- ing waste treatment facility (lagoons) as well as re- organizing the ISLSU line was sought in this study. Fig. 1. The solid–liquid separation system. 2. Assessment of the existing situation In accordance with the stated objective a detailed sur- vey of the amount and the quality of waste waters was These streams are insignificant in volume as compared undertaken within this project and the performance of to flume waters. the ISLSU, as well as the lagoons, were assessed. The coarse solid, grit and pulp removers were found func- 1.2. Lagoon system tioning properly and no problems could be identified regarding the efficiency of these. However, the rectangu- The underflows from the settling basins are merged lar settling basin comprised of cells was found to be inef- and then sent to the lagoon system which is composed fective in settling the suspended solids in that arrange- of three basins connected in series, namely, a sludge ment. The circular sedimentation basin located before accumulation basin, a facultative basin and an aerated the rectangular settling basins was found operating with lagoon discharging its contents to a nearby river, as a hydraulic detention time of 1.17 h and receiving a sol- shown in Fig. 2. The capacity of the sludge accumulation ids load of 7.3 kg/m2/h, was discharging relatively dilute basin, which was around 64 700 m3 in volume, was found insufficient to settle all the incoming solids during Table 1 a sugar campaign which usually lasts for 5 months. Typical characteristics of the effluent from the previous lagoon system Hence, subsequent stages of the lagoon system were receiving a waste stream with an extremely high solids Parameter Concentration (mg/l) Discharge limit (mg/l) load and were consequently lowering the treatment per- formance. The typical effluent quality values from the BOD5 600 50 lagoon system discharging into the nearby receiving COD 2500 500 Suspended solids 200 100 river prior to the rehabilitation works are shown in Table Fig. 2. The previous lagoon system. F.B. Dilek et al. / Journal of Cleaner Production 11 (2003) 327–331 329 Table 2 3. Rehabilitation of the existing facilities The previous performance of the settling basins 3.1. Solid–liquid separation system Circular settling Rectangular basin basin of 4 in-series cells To be able to use the sedimentation basins as effec- Inflow (m3/h) 2300 2150 tively as possible, a variety of operational schemes has Surface area (m2) 2117 255.4 (each cell) been designed and checked on the basis of hydraulic and Hydraulic loading rate 26.1 202.0 solids loading rates. Although the first circular sedimen- 3 2 (m /m .day) tation basin was discharging a relatively dilute under- Hydraulic retention time (h) 1.17 0.42 (each cell) Solids loading rate (kg/m2.h) 7.3 10.2 (first cell) flow, it was decided that the most practicable operation Underflow to lagoon system 150 100 of this unit would be the existing flow scheme. However, (m3/h) calculations indicated that the rectangular sedimentation Underflow solids 1.6 7.9 basin comprised of four in-series rectangular cells was concentration (%) operating with a very low solids loading rate and with Underflow solids to lagoon 2500 7900 system (kg/h) a very high hydraulic retention time. Therefore the oper- ation sequence of this unit was changed from in-series to in-parallel mode. It was found that only two of the cells operating in parallel would be sufficient for underflow. On the other hand, the rectangular settling efficient solids removal. The remaining two cells were basin, which was comprised of four in-series rectangular then to be used for thickening underflows from the earl- cells, was operating with low solids loading rate and ier settling stages, as depicted in Fig. 3. In this way, it with an extremely high hydraulic loading rate as shown would be possible to concentrate sludge going to the in Table 2. The total sludge flow into the lagoon system lagoons and in turn recycling more water within the (250 m3/h) was about 11% of the flume water entering plant. Consequently, the sludge flow rate going to the 3 into the ISLSU. Thus, there was a considerable loss of lagoons dropped down to 85 m /h from the earlier 250 3 water that could be circulated within the factory. m /h value, which also reduced the load pressure on the The composite effluent reaching the lagoons was lagoons with concomitant improvement in the effluent highly concentrated in terms of organic matter, as shown quality. in Table 3. Considering that the lagoons were designed for a lower hydraulic and solids loading, they were 3.2. Lagoon system clearly overloaded and were not functioning properly. This, in turn, reflected poorly upon the quality of the The lagoon system was re-evaluated under the effluents. reduced load conditions. A new operational scheme was Thus, it appeared that in the up-stream the problem implimented and the whole process was re-designed was arising mainly from the inefficient rectangular set- accordingly [2]. The disused, so-called, filter cake pond tling basin within the ISLSS. On the down-stream end was included in the operational lagoon system to serve the poor effluent quality was due to the improperly as the primary sludge sedimentation basin.