Water Journal : Water Journal November 2012-1
refereed paper odour management water NOVEMBER 2012 59 of the headspace gases into the GC inlet using a gas-tight syringe (Glindemann et al., 2006). Although this method has been reported to be representative of the biosolids storage pile interior, easy to use and highly reproducible (Glindemann et al., 2006), manual injections of the headspace gases into the GC inlet are time consuming and laborious, and limited to analysis of only a few samples. Solid-phase microextraction (SPME) has been used in the analysis of trace levels of volatile organic sulphur compounds as well as other volatile organic compounds (VOCs) in various matrices, such as aqueous (e.g. Kristiana et al., 2010), headspace (e.g . Kim et al., 2002) and ambient air (e.g . Haberhauer- Troyer et al., 1999). This technique is rapid, relatively inexpensive, easily automated and solvent-free. It also allows for minimal sample handling, which is highly desirable in the analysis of volatile compounds. In this procedure, the analytes of interest are adsorbed onto a thin polymer film or porous carbonaceous materials that are bonded to a fused silica fibre (SUPELCO, Bulletin 923, 1998; Visan and Parker, 2004). Ideally, equilibrium is reached between the odour matrix and fibre, but for accuracy and precision, consistent sampling time, temperature and fibre immersion depth are more important than equilibrium (SUPELCO, Bulletin 923, 1998; Visan and Parker, 2004). SPME is compatible with analyte separation/detection by GC-MS or HPLC and gives linear results for wide concentrations of analytes. When SPME is coupled with GC-MS, the analytes adsorbed onto the fibre are released by way of thermal desorption in the vapourising injector port of the GC and are transferred onto the GC column (Pawliszyn, 1997). By controlling the polarity and thickness of the coating on the fibre, maintaining consistent sampling time, and adjusting several other extraction parameters, highly consistent and quantifiable results can be obtained from low concentrations of analytes (SUPELCO, Bulletin 923, 1998). SPME coupled with GC-MS has been used for the analysis of odorous compounds in several biosolids projects. For example, Turkmen et al. (2004) have reported the use of SPME-GC -MS for the analysis of DMS, DMDS, methyl merceptan, H 2S, CS2, trimethylamine and dimethylamine in anaerobically digested wastewater sludge. However, this method required the use of a complicated set-up for SPME calibration and sampling of the gaseous odorants. Visan and Parker (2004) used SPME-GC -MS for the analysis of TMA, DMS, DMDS and methyl mercaptan in stored biosolids. This method used permeation devices and complicated apparatus for sampling of gaseous standards of the odorants and involved manual injection of the SPME fibre into the GC injector (Vissan and Parker, 2004). In this study we have used SPME- GC-MS for the analysis of odorous compounds in the headspace of wet biosolids. In this method the biosolids samples were analysed as “aqueous” samples. This method does not require any complex sampling equipment, is reproducible and the analysis is fully automated, allowing for a higher throughput of samples. Project Aims The aims of this study were to: (1) determine the most suitable odour reduction strategy for biosolids produced at our test site and (2) develop analytical methods to identify the chemical compounds responsible for the odour in biosolids from our test site and to assess the effectiveness of the trialled odour reduction measures. In this paper we present the results from Phase I laboratory scale trials of chemical addition and centrifuge speed trials as means of odour reduction. The methodology used to conduct these trials and to identify the odorous compounds is also described. The Test Site Woodman Point WWTP (Figure 1) in the Perth metropolitan area was chosen as the test site for this study. The key driver for choosing Woodman Point was that the produced sludge and biosolids were perceived to be more odorous compared to similar materials produced at other treatment plants. Additionally, during the course of the project Woodman Point was less likely to have interruptions in the sludge handling/production process. The plant was also easy to access and sample, and it has the most current technology for processing sludge. The plant typically handles between 120–140 million litres of wastewater per day (120– 140ML/d) with 99% of the wastewater being derived from households (Water Corporation, 2012). It is an activated sludge plant that uses sequencing batch reactors (SBR) and egg-shaped digesters (Figure 2) to process the sludge. The advantage of using SBR over the conventional aeration tank systems is that the biological treatment and clarification are completed in a single step, thereby reducing costs and space (Water Corporation, 2012). The egg- shaped digesters are operated in the mesophilic range (35–37°C) and offer several advantages over the conventional cylindrical anaerobic digesters, namely better mixing and heating. The digester feed is a 1:1 mixture of primary sludge and waste-activated sludge with a typical dry solids (DS) content of 4–6% and the average solids retention time (SRT) is > 20 days. The digested sludge (dry solids content of 2–4%) is then dewatered using high solids centrifuges. The resulting dewatered biosolids cake has a dry solids content of approximately 17–19% (Water Corporation, 2012). Materials and Methods Chemicals and materials Anaerobically digested sludge (DS 3.7%, SRT 19 days) and plant-dewatered biosolids cake (DS 16.9%) samples were obtained from Woodman Point WWTP. Polymer used for dewatering was a powder polymer FO4800SSH from SNF (supplied by Water Corporation) with a molecular weight of approximately 8 million and a charge density of 80%. Aluminium sulphate and polyaluminium chloride, used in the chemical addition trials, were sourced from water treatment Figure 1. An aerial view of Woodman Point WWTP, Perth, Western Australia.
Water Journal December 2012
Water Journal September 2012-1