Water Journal : Water Journal November 2012-1
odour management refereed paper technical features 60 NOVEMBER 2012 water plant operations at Water Corporation of Western Australia (WCWA). Aluminium sulphate was used as a 56% w/v solution. Polyaluminium chloride (PAC23 from Orica) was used as a 23% w/v solution in aluminium oxide. Ferric chloride was used as a 36% w/v solution, prepared in-house from analytical grade ferric chloride (Sigma-Aldrich). Analytical standards for: sodium thiomethoxide, ethanethiol, DMS, DMDS, DMTS, ethyl methyl sulphide (EMS), diethyl disulphide (DEDS), toluene, ethylbenzene, styrene, p-cresol, indole, skatole and geosmin were purchased from Sigma-Aldrich at purity ≥ 99%. Deuterated dimethyl disulphide (DMDS-d6) was purchased from Sigma- Aldrich. Deuterated ethylbenzene (ethylbenzene-d10) was purchased from Cambridge Isotope Laboratories Inc. Methanol was HPLC grade from Fischer Scientific. Anhydrous granular sodium sulphate was purchased from Ajax Finechem and was baked at 400°C for a minimum of four hours prior to use. Two SPME fibres were used: 50/30 μm divinylbenzene-carboxen- polydimethylsiloxane (DVB-CAR-PDMS) and 65 μm polydimethylsiloxane- divinylbenzene (PDMS-DVB). Laboratory scale dewatering For our laboratory-scale dewatering procedure, 600–800g of digested sludge in a 1L glass beaker was stirred at 200rpm for 30 seconds using a jar tester. A polymer solution (0.3% w/v; polymer dose was based on the average amount used at Woodman Point WWTP) was added and the resulting mixture was stirred at 200rpm for another 30 seconds and then stirred at 50rpm for 90 seconds. This mixing regime was based on the mixing regime reported by Higgins (2010). The sludge mixture was then dewatered using a laboratory centrifuge (Heraeus Multifuge 3S with a maximum rotational radius of 18.2cm) at 3850rpm for 20 minutes. The combined wet cake was then pressed between two medium- density fibreboards (MDF) (300mm x 300mm; 7mm thick) encased in polyethylene wrap and lined with sheets of Whatman No 1 filter paper to absorb the excess water. Pressure was applied by placing weights totalling approximately 8kg on top of the MDF boards. To simulate the high shear experienced in the plant centrifuge, the sample cake was processed through a manual food mincer (Avanti food mincer #8) which pushed the cake through a “scroll- conveyor”, followed by extrusion through several openings, each 8mm in diameter. The lab-dewatered biosolids cake had a similar texture and odour to the plant dewatered sample. The solids content of the lab-dewatered cake was comparable to that of the plant dewatered cake. Chemical addition to digested sludge prior to dewatering Individual samples, of anaerobically digested sludge (approximately 800g each) in 1L glass beakers, were treated with aluminium sulphate (alum), polyaluminium chloride and ferric chloride atdosesof2%and4%ofmetalonadry weight basis. The samples were mixed using a jar tester. The mixing regime used was based on that reported by Higgins (2010) and is shown in Figure 3. A control sample, with no chemical addition, was also prepared. The samples were dewatered using the dewatering procedure described above. The resulting biosolids cake samples (approximately 200g) were incubated at room temperature in 1L Schott bottles. The samples were wrapped in aluminium foil to protect from light and were monitored for evolution of sulphur compounds (DMS, EMS, DMDS, DEDS and DMTS) by HS SPME-GC-MS every other day for 20 days. The samples were also analysed for the production of OVACs (toluene, ethylbenzene, styrene, p-cresol, indole, and skatole) by HS SPME-GC-MS weekly for 37 days. Chemical addition to plant-dewatered cake Samples of the plant dewatered biosolids (approximately 85g) in 400mL glass beakers were treated with aluminium sulphate hydrate at doses of 2% and 4% of metal on dry weight basis and mixed manually with a stainless steel spatula for approximately two minutes. A control sample (no chemical addition) was prepared in the same way. The cake samples were incubated at room temperature in 250mL Schott bottles. Samples were wrapped in aluminium foil to protect from light and were monitored for evolution of sulphur compounds by HS SPME-GC-MS every other day for 14 days. The samples were also analysed for the production of OVACs by HS SPME-GC-MS weekly for 16 days. Figure 2. Egg-shaped digesters at Woodman Point WWTP. At 38 metres high, they are the largest of their type in the Southern Hemisphere. Chemical Addition Mix 200 rpm, 30 s Polymer Addition Mix200rpm,30s Mix50rpm,90s Dewatering Figure 3. Mixing regime used in trials of chemical addition to digested sludge.
Water Journal December 2012
Water Journal September 2012-1