DEWATERING DRINKING WATER SLUDGE S IN REED BED SYSTEMS Nielsen, S 1. and Cooper D.J., 2 1 Orbicon A/S, Denmark,

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1 14 th European Biosolids and Organic Resources Conference and Exhibition 1 DEWATERING DRINKING WATER SLUDGE S IN REED BED SYSTEMS Nielsen, S 1. and Cooper D.J., 2 1 Orbicon A/S, Denmark, 2 ARM Ltd, UK Author s smn@orbicon.dk; info@armreedbeds.co.uk Abstract Sludge drying reed beds have been used for dewatering and mineralisation of sewage sludge s since the late 198 s, however there has been no experience of treating drinking water sludge s in reed bed systems. Water Treatment Works (WTW) treat water to a potable standard, part of this treatment includes dosing with Iron Sulphate to help dirt particles to coagulate, producing a ferric sludge. Historically the sludge wastes have been pumped to the sludge lagoons at Hanningfield Reservoir. However, these are now nearing the end of their serviceable life and a new sludge handling process is required. As part of a trial with Essex and Suffolk Water, ARM Ltd and Orbicon A/S set up a series of six trial beds, each 2m 2 at Hanningfield Reservoir in Essex to examine the dewatering processes of the sludge produced from the water treatment process. These were monitored from The purpose of the test is to clarify whether the sludge is suitable for treatment in a sludge reed bed system, the dimensions criteria and the quality of reject water from the sludge reed bed system. The operation of the test system has been very positive especially because of the very intensive loading program for some of the basins on such a young system. It is possible to drain and treat ferric sludge (approximately 3, mg Fe/kg dry solid) in a reed bed system. The system has a good draining efficiency and the filtrate water from the sludge loading is out of the system the next day. The sludge residue surface is drying as indicated by evidence of desiccation cracks shortly after the water drains out of the system. In spite of the different loading programs, volume reduction is very high at over 99%. The ferric sludge is dewatered to approximately 3-4 % dry solid and desiccates in the trial beds. It is possible to get the vegetation to grow in ferric sludge, where the ph was measured to 7, 7. It has not been necessary to use fertilizer. The proposed use of reed bed systems not only reduces the capital and operating cost, but also provides the site with an environmental friendly operation area. The overall reduction of the sludge volume occurs without the use of chemicals. The process involves only a very low level of energy consumption for pumping the sludge and reject water. Key words Sludge treatment, reed bed System, drinking water sludge, load, dewatering, ferric sludge Introduction It has been identified by the asset management strategy for Essex and Suffolk Water that there is a need to provide a new process for sludge handling at the Hanningfield Water Treatment Works.

2 14 th European Biosolids and Organic Resources Conference and Exhibition 2 Hanningfield WTW (Figure 1) is supplied with raw water from Hanningfield Reservoir. The existing treatment works comprises pre-ozonation, clarification, filtration, main ozonation, pesticide removal, chlorine disinfection prior to the pumping of treated water. Sludge waste is generated primarily from the de-sludging of the Pulsator clarifiers producing a mineral sludge with seasonally fluctuating levels of algae and suspended solids. Figure 1 Hanningfield Water Works and the water works sludge lagoon The final part of the solids removal process is the rapid gravity filters and the granular activated carbon contactors used during backwashing. Historically these sludge wastes have been pumped to the sludge lagoons at Hanningfield Reservoir. However, these are now nearing the end of their serviceable life and a new sludge handling process is required. The two options being considered are a mechanical centrifugal solution and sludge treatment reed beds. The proposed use of reed bed systems not only reduces the capital and operating cost, but also provides the site with an environmentally friendly operation area. The purpose of the trial is to clarify: Whether the sludge from Hanningfield Water Treatment Works is suitable for further treatment in a sludge reed bed system. The dimensions required (capacity, operations, loads, area, number of basins, etc.) for a full scale plant at Hanningfield Water Treatment Works. The quality of reject water from a sludge reed bed system treating sludge from Hanningfield Water Treatment Works.

3 14 th European Biosolids and Organic Resources Conference and Exhibition 3 Historically, sludge reed beds (Figure 2) have been used for the dewatering and mineralization of sewage sludge in Europe since The European Union Water Framework Directive calls for cleaner discharges from our waste water treatment facilities. Improved treatments to achieve higher quality effluents results in the production of more sludges. In countries like Denmark, France, Germany and Sweden, sludge treatment in Reed Bed Systems are a common and a well-proven method. Long-term sludge reduction takes place in reed-planted basins, partly due to dewatering (draining, evapotranspiration) and partly due to mineralisation of the organic solids in the sludge. Sludge from wastewater treatment plants is pumped onto the basin surface. The dewatering phase results in the dry solids content of the sludge remaining on the basin surface as sludge residue, whereas the majority of its water content continues to flow vertically through the sludge residue. The water content is further reduced through evapotranspiration. Figure 2 Sludge reed bed system A sludge treatment reed bed system utilizes the forces of nature to reduce and treat sludge. The only appreciable power consumption is by the pumps used to transport sludge and reject water. This means that the reed bed system uses much less power than other systems. Transport costs will be reduced substantially, while the volume of sludge can be reduced to approximately % of its original volume. The sizing and design of reed bed systems depends on the sludge production (TDS per annum), sludge type, quality and regional climate. The treatment period is approximately 8-12 years and the operation of the system may be divided into a number of phases related to different periods in the lifetime of a system. Each phase consists of commissioning, full operation, emptying and reestablishment of the system. When the system is setup, it requires only a weekly control-visit to the site of about one to two hours, and there is no contact with the sludge, which gives a better working environment. The plan is to empty the Sludge Reed Bed System over a period, with 2-3 basins selected for emptying per year. Capacity during the emptying period is maintained despite the reduction in number of the basins the emptying phase. After a period of years, the basins are emptied, and its contents can be recycled and spread on farm land. After a basin has been emptied you can start the load for another operations period. Maintaining full capacity during emptying is possible provided that the basins are re-established after emptying with

4 14 th European Biosolids and Organic Resources Conference and Exhibition 4 sufficient regeneration of vegetation, and provided that the loading rate is adapted to vegetation growth. So re-planting basins has not been necessary. Sludge treatment in reed bed systems is a thoroughly tested method with a number of proven advantages. The overall reduction of the sludge volume occurs without the use of chemicals. The process involves only a very low level of energy consumption for pumping the sludge and reject water resulting in a minimum of CO 2 -emissions. The control system (SCADA) can be setup at the main working site and the daily surveillance can be done from there. There is no noise from the system as there is from many other types of treatment systems. The system works effectively to reduce pathogenic bacteria like Salmonella, Enterococci and E. Coli, thus making it a lot safer to be on site. Sludge treatment in Reed Bed Systems uses no chemicals in the dewatering process. This means a considerable improvement in the working environment along with a reduction of the chemical residue in the treated waste water passing into the environment. The content of substances in sludge that are foreign to the environment can be reduced. After the treatment of sludge, recycling options are good, particularly in agriculture. The sludge quality is cleaner and more adaptable in the natural cycle than mechanically dewatered sludge. Methods and results The Hanningfield test system (Figure 3) was built at Hanningfield Water Treatment Works with 6 basins each of 2m 2 with a design comparable to a full-scale system with reeds, ventilation, sludge input; reject water systems as well as filters and drains. The reeds were planted in February 28. The development during 28 was good. The reeds grew well and began to cover the whole surface and achieved a height of approximately 1 meter. It hasn t been necessary to replant as the reeds have thrived in the test system. In 29 the reed growth continued and the surface of the basins was approximately 1 % covered with reeds. In July the reeds had achieved a height over 2 meters (Figure 4). It has not been necessary to add fertilizer.

5 % 14 th European Biosolids and Organic Resources Conference and Exhibition 5 Figure 3 Basin no (Hanningfield Sludge Treatment System) Sludge quality The data (Figure 4) shows that there is a large variation in the total solids being loaded into the basins. Therefore it is very important to know the % of dry solid in each load in order to calculate the load (kg ds/m 2 /year) as precisely as possible. The contents of solids are lower in 29 and it has been necessary to adjust the loading program to achieve the demanded area loads. The sludge quality seems to have good sedimentation ability (Figure 5) and settles well within a few minutes.,6,5 Total Solids Average 28:,186 29:,163,4,3,2, Figure 4 Total solid (%) Sludge

6 m3 14 th European Biosolids and Organic Resources Conference and Exhibition 6 A B B A Figure 5 Sedimentation of the sludge. A: Sludge sample ( ). B: Sedimentation period. Load The basins have been loaded for approximately 7 and 4 months in 28 and 29, respectively. During the test period the load has been intensified. Each load representing a volume of 3m 3, has been loaded over a period of approximately 1 hour. The accumulated volume has resulted in a total loaded volume of m 3 and m 3 in 28 and 29 (as of ), respectively (Figure 6). The dry solid content in the sludge has varied during the test. The average values were.18 % and.16 % in 28 and 29, respectively (Figure 5). The accumulated load has resulted in a total load of 11-3 kg and 7-24 kg in 28 and 29 ( ), respectively. During the test-loading period in 28, each of the basins have been loaded for 1-3 days (loading days) with 1-4 batches daily, followed by a rest period of approx. 1-3 days (resting days). In 29 the basins have and will be loaded for 2-5 days with 2-4 batches daily, followed by a rest period of approx days Loading basin Figure 6 Load of basin no 1 (m 3 )

7 m3/h l/sec/m2 14 th European Biosolids and Organic Resources Conference and Exhibition 7 In 28 the area load had been applied for a whole year the area load would have varied between 1 to 26 Kg ds/m 2 /year. In 29 the area load was varied between an area load 25 5 kg ds/m 2 /year for a whole year. 4,5 4 3,5 3 2,5 2 1,5 1,5 Basin no 1,25 Inlet Outlet,2,15,1,5 -, : : : Figure 7 Four loads and the resulting dewatering profile. Dewatering (l/sec/m 2 ) The majority of the water in a sludge load continues to flow vertically through the sludge residue and filter. The dewatering (liters/second/m 2 ) is good (Figure 7 and 8). The dewatering efficiency has a positive development in 29. The basins are now more mature with a good crop of reeds. The decrease in the dewatering profile has not been so pronounced and the variation in the dewatering efficiency from the basins has been reduced. The load has increased in 29 for all the basins. The maximum loads are 2-4 loads per day per basins (approx m 3 /day).,5 BASIN 6 Reject (l/s/m 2 ),45,4,35,3,25,2,15,1, Figure 8 Reject water from the basin no. 6 (Liters/second/m 2 )

8 % 14 th European Biosolids and Organic Resources Conference and Exhibition 8 Generally the dewatering profile is a peak with a maximum over.15 l/sec/m 2. In some basins the maximum dewatering speed is over.2.25 l/sec/m 2 (Figure 8). Dewatering (m 3 ) The times for dewatering of 6-12 m 3 are approximately 15 hours and over 9 % of the load is dewatered in that period (Figure 9). Other positive results are that the dewatering profiles generally are very narrow, short, steep (up and down) and reach the bottom line with a short period of time, even for the basins which had been loaded with 12 m 3 each day for 4 days Reject - % of load Average system Basin no. Figure 9 Volume of reject water - percentage of load (basin no 1-6) Dewatering Volume reduction The dewatering phase results in the dry solids content of the sludge remaining on the basin surface as sludge residue. The water content is further reduced through evapotranspiration. The sludge residue shows evidence of desiccation very quickly (Figure 1). In spite of the different loading programs, volume reduction is very high over 99 %. In 29 the reduction is slightly higher than in 28 with an increase in the loads (Table 1), and with more mature basins. The dry solid ( ) in the sludge has been concentrated approximately 2 times to a dry solid estimate in the sludge residue of approximately % (Table 1). Table 1 Reduction in sludge volume Bassin no. Sludgevol. Sludge dry solids (%) Reduction Sludge Sludge residue dry m 3 % residue solids (%) Min. Max. Avg. vol. Min. Max. Avg m 3

9 14 th European Biosolids and Organic Resources Conference and Exhibition 9 Figure 1 Dewatering efficiency and change in the sludge surface in 14 days (September/October 28) Reject Water - Quality The dewatering phase results in the dry solids content of the sludge remaining on the basin surface as sludge residue. Samples of Water Works sludge and samples of reject water treated in the reed bed system show the efficiency of the filtration through the reed beds (Figure 11). Samples of sludge and reject water taken in the hours after the sludge load. Sludge treatment in the reed bed system showing the high efficiency of the filtration. The quality of the reject water during the hours after the loading has a very low content of suspended solid after one load. More than one load on the same basin on the same day results in turbidity variations in the reject water (Figure 11). Figure 11 Sludge samples (A) and samples of reject water (1, 2, 3, 4,) during a period with first 3 of 4 loads

10 NTU 14 th European Biosolids and Organic Resources Conference and Exhibition 1 Turbidity - Total Figure 12 Reject water Turbidity (NTU) In May 29 a turbidity meter was installed on the outlet pipe. The data recording started in May (Figure 12) before it was calibrated in May and early June. In the initial period before the meter was calibrated it shows incorrect values. Generally since June the turbidity is lower than 5 NTU (Figure 13). During the loading (eg. 4 loads in one day) there is an increase in the turbidity, up to approximately 2 NTU. A few results reach 5 NTU. The trend shows that the main volume of water has a turbidity level below 5 NTU even in the loading periods (Figure 12). Sludge residue Sludge residue levels are measured approximately every 14 days. There has been a reduction in depth from 12 to 6 cm over a period of approximately 15 weeks which indicates the effect dewatering in the resting period (Figure 13). The results have shown that the system has good dewatering properties resulting in good dry solid %. The amount of nitrogen and phosphorus in the sludge residue appears at present, to be sufficient to support reed growth (Table 2).

11 cm 14 th European Biosolids and Organic Resources Conference and Exhibition Basin 1 Average depth gauge 1-3 Scale pole Figure 13 Table 2 Basin no 1 - Sludge residue height Sludge residue quality in the lagoon and in the basins ( ). The numbers in the bracket are days since last load Parameters Unit Basin 1 Basin 2 Basin 3 Basin 4 Basin 6 Lagoon Site 1 Lagoon Site 2 Dry solid % 39 (21) 4 (18) 44 (28) 42 (4) 31 (6) Loss on ignition Total nitrogen Total phosphor % of DS mg/kg DS 4,8 7,2 7,9 8,6 7,6 5,3 3,9 mg/kg DS 11, 1, 9,7 9,6 8,1 9,1 58, Aluminium mg/kg DS 1,7 1,4 1,4 1,3 2,2 4,1 2,7 Calcium mg/kg DS 47, 47, 46, 43, 5, 16, 2, Iron mg/kg DS 37, 39, 39, 37, 37, 23, 13, FeS 2 (pyrite) mg/kg DS ,9 25 Grease + Oil mg/kg DS < Conclusions In the first phases (March 28 January 29) of the test the results have shown that: 1. The operation of the test system has been very positive especially because of the very intensive loading program for some of the basins on such a young system. 2. The reeds are approximately 2. meters high and they are beginning to cover the whole surface.

12 14 th European Biosolids and Organic Resources Conference and Exhibition The filters have a good draining efficiency and the water from the loads is out of the system the next day. The sludge residue is dewatered to approximately 3-4 % dry solid. 4. Shortly after the water is out of the system the sludge residue surface is cracking up very well. 5. The dewatering is good. 6. Samples of the reject water have shown that the filter has a good filtration capability. 7. A full scale system will need 16 basins and the loading can be 3 kg dry solid/m 2 /year. References Nielsen, S. (23) Sludge Drying Reed beds. Water Sci. and Technology.48, No 5 pp Nielsen, S. (23) Paper: 16 years of experience with sludge treatment in Reed beds system Conference: Achievements and Prospects of Phythoremediation in Europe. COST Action October 23 Vienna. Nielsen, S.(25) Sludge Reed beds facilities: Operation and problems. Water Sci. and Technology, 51 No 9 pp Christensen, L.B. (1991) Acidification and Ochre formation in Fenlands. BSSS and IPS Symposium, Cambridge, England April Acknowledgements The authors do wish to thank the different partners involved in this study: Essex & Suffolk Water, Hanningfield Treatment Works, and Northumbrian Water Limited.