Foam-aided sludge treatment

Transcription

1 Foam-aided sludge treatment 1 st International IWA Conference on Holistic Sludge Management 6-8 May Västerås Karita Kinnunen, Jani Lehmonen, Tuomo Hjelt, Pentti Pirkonen VTT Technical Research Centre of Finland

2 2 Content Drivers & Motivation Foam as a enhancing aid Static methods and results Dynamic methods and results Conclusions

3 3 DRIVERS AND MOTIVATION

4 4 Drivers to the effective sludge treatment 11 million tds/a sludge in EU from municipal waste water plants The legislation has been tightened Increasing industrial productions -> increasing quantities of sludge High treatment costs High landfill costs o In EU soon organic matter such as waste water sludge is not allowed to landfill at all High demand to sludge minimisation Can be done by 1)Lowering the amount of water in the final sludge cake 2)Decreasing the generation of sludge in WWTP process Usually done by using different filter aids to create water channels inside the filter cake during filtration. o commercial filter aids, residue based fly ash, classified ash, cement kiln dust, gypsum, fine coal, lignite, rice hull ash.

5 5 Motivation: Boiler efficiency as function of Kattilahyötysuhde polttoaineen kosteuspitoisuuden funktiona moisture content 93, ,5 Boiler efficiency [%] Hyötysuhde [%] 92 91, ,5 90 1%-point change in boiler efficincy of 400 MW th boiler ~ 40 GWh more fuel is needed (= per year) 89, , Moisture Kosteus content [%] [%] Source: Janne Kärki, VTT

6 6 Foam as a enhancing aid in a sludge treatment

7 7 Foam used as a filter aid The method is based on the technology validated on a pilot paper machine Basic idea: Small amount of foam is applied to the surface of the sludge Foam bubbles are sucked through the sludge cake Channels are produced to the structure that enhance the water drainage Increase in DS content in the sludge cake Decrease in the time of filtration Decrease in the turbidity of the filtrate. This implicates that the retention of micro scale particles was enhanced effectively.

8 8 STATIC METHODS AND RESULTS

9 9 Static set-up Bio sludge from a mill producing both pulp and paper, the dry solid content 1.2%. Fennopol K1390 as a flocculation polymer, 5 kg/tds Foam: o water and anionic surface active agent (sodium dodecyl sulphate, SDS), 2.5 g/l o density 100 g/l o applied to the top of the sludge before drainage Average vacuum level in the funnel 0.5 bars

10 10 Increased dewatering rate Foam increased 50% of the filtrate rate in 60 s of vacuum filtration compared to the reference.

11 11 Results from the static experiments Cleaner filtrates from the foamassisted sludge vacuum filtration 10% lower weight of the cake in foamassisted experiments An example of the filtrate cake in FAD

12 12 DYNAMIC METHODS AND RESULTS

13 13 Dynamic set-up A foam generator A dynamic thickening unit: a feeding line with a feed pump free and vacuum-assisted dewatering sections, lengths 90 and 410 mm an adjustable wire device the length of the sludge web was 95 mm the average vacuum level around 2 kpa -> thickening instead of filtering

14 14 Foam formation Water and foaming agent are mixed with pressurized air using a foam generator Air content greater than 80%, preferably 90-95% The foam generator Rotor-stator mixing heads

15 15 Optimum foam application position Foam application was just before the dewatering section The highest dry solids content In all cases to the turbidity of filtrates was also lower

16 16 Influence of polymer dosages on the thickening of the cake Bio sludge from a mill producing both pulp and paper The foam application position was fixed based on the earlier results Fennopol K1390, 0.95 kg/tds and 1.9 kg/tds dosed online before a headbox feed pump Foam, density of 100 g/l, was produced online by a foam generator sodium dodecyl sulphate (SDS), 2.5 g/l For reference: the flocculated sludge was thickened without using the foam

17 17 Increase in dry solids content of the cake The increase in the lower polymer addition level was around 10%, the same as in the case of the static filtration

18 18 Enhanced micro scale particle retention Polymer dose 1.9 kg/tds: 80 NTU -> 43 NTU (~50%) Polymer dose 0.95 kg/tds: 215 NTU -> 89 NTU (>59%) Possibility of chemical optimization in the sludge foam-assisted thickening Foam: An air content of 90% The layer thickness 5-10 mm, corresponding to a mm water layer No dilution effect of foam on the filtrates

19 19 CONCLUSIONS

20 Conclusions of the foam-assisted dewatering experiments 20 Applicable for sludge thickening and vacuum filtration processes. The dry solid content of the filter cake was increased by 10% compared to filtration without foam. The rate of the dewatering was significantly increased, indicating savings in the dewatering energy or increase in the capacity of the filter. Turbidity of the filtrate clearly decreased, indicating an enhancement of the retention of micro-sized particles.

21 21 Conclusions of the foam-assisted dewatering technology Results obtained in this study may be valuable in the dewatering of WWTP sludge and industrial slurry. More experiments should be performed using industrial slurries and different dynamic belt filtering techniques. The expected benefits could be: a higher dry solid content of filter cake cleaner filtrates a faster dewatering rate lower flocculent consumption.

22 22 Foam aided sludge treatment enables 1. Savings on drainage energy 2. Increase the capacity of the filtering device 3. Enhancement in retention of the micro sized particles

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