In this study, a short pre-aeration step was investigated as pre-treatment for thermophilic anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). It was found that pre-aeration of 48 hours generated enough biological heat to increase the temperature of bulk OFMSW to 60 o C. This was sufficient selfheating of the bulk OFMSW for the start-up of thermophilic anaerobic digestion without the need for an external heat source. Pre-aeration also reduced excess easily degradable organic compounds in OFMSW, which were the common cause of acidification during the start-up of the batch system. Careful consideration however must be taken to avoid over aeration as this consumes substrate, which would otherwise be available to methanogens to produce biogas. To accelerate methane production and volatile solids destruction, the anaerobic digestion in this study was operated as a wet process with the anaerobic liquid recycled through the OFMSW.Appropriate anaerobic liquid inoculum was found to be particularly beneficial. It provided high buffer capacity as well as suitable microbial inoculum. As a result, acidification during start-up was kept to a minimum. With volatile fatty acids (VFAsacetate in particular) and H 2 accumulation typical of hydrolysis and fermentation of the easily degradable substrates during start-up, inoculum with high numbers of hydrogenotrophic methanogens was critical to not only maximise CH 4 production but also reduce H 2 partial pressure in the system to allow VFAs degradation. In a lab scale bioreactor, the combined pre-aeration and wet thermophilic anaerobic digestion was able to stabilise the OFMSW within a period of only 12 days. The stabilised inert residual material can be used as a soil amendment product.3 of 32

The biological stabilisation of the organic fraction of municipal solid waste (OFMSW) into a form stable enough for land application can be achieved via aerobic or anaerobic treatments. To investigate the rates of degradation (e.g. via electron equivalents removed, or via carbon emitted) of aerobic and anaerobic treatment, OFMSW samples were exposed to computer controlled laboratory-scale aerobic (static in-vessel composting), and anaerobic (thermophilic anaerobic digestion with liquor recycle) treatment individually and in combination. A comparison of the degradation rates, based on electron flow revealed that provided a suitable inoculum was used, anaerobic digestion was the faster of the two waste conversion process. In addition to faster maximum substrate oxidation rates, anaerobic digestion (followed by post-treatment aerobic maturation), when compared to static composting alone, converted a larger fraction of the organics to gaseous end-products (CO 2 and CH 4 ), leading to improved end-product stability and maturity, as measured by compost self-heating and root elongation tests, respectively.While not comparable to windrow and other mixed, highly aerated compost systems, our results show that in the thermophilic, in-vessel treatment investigated here, the inclusion of a anaerobic phase, rather than using composting alone, improved hydrolysis rates as well as oxidation rates and product stability. The combination of the two methods, as used in the DiCOM ® process, was also tested allowing heat generation to thermophilic operating temperature, biogas recovery and a low odour stable end-product within 19 days of operation.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights: A pilot scale biofilter removed H2S and NH3 in a wastewater treatment plant. The biofilter produced small volume of leachate which contains ammonium sulphate. The ammonium sulphate produced can be harvested for further use. AbstractBiofilters are popular for the removal of odours from gaseous emissions in wastewater treatment plants because of their low capital costs and low energy requirements. In an aerobic environment, the microbes in biofilter oxidize odorous gases like hydrogen sulphide (H2S) and ammonia (NH3) to non-odorous sulphate and nitrate. This paper describes a pilot plant biofilter setup at a local waste water treatment plant (WWTP) which has been in continuous operation for more than 150 days, removes both H2S and NH3 at an average removal efficiency of 91.96% and 100% respectively. Unlike a conventional biofilter, the pH of this biofilter was not adjusted by addition of chemicals or buffers and the H2SO4 produced from the biological conversion of H2S is periodically washed down and allowed to accumulate in a concentrated form at the base of the biofilter. NH3 entering at the base is removed, not by biological oxidation, but by the chemical reaction of ammonium with sulphate to form ammonium sulphate. The ammonium sulphate produced in biofilter is washed down and the volume of leachate produced is less than 0.2mL of leachate/L of reactor/day. Estimated cost savings of converting the current chemical scrubber used at the WWTP to a similar biofilter described in this study is included with this paper.

The Woodman Point Wastewater Treatment Plant (WWTP) at Western Australia has experienced two separate problems causing avoidable maintenance costs, the build-up of massive struvite (MgNH 4 PO 4 . 6H 2 O) scaling downstream of the anaerobic digester and the formation of hydrogen sulfide (H 2 S) levels in the digester gas to levels that compromised gas engine operation and caused high operating costs on the gas scrubber. As both problems hang together with a chemical imbalance in the anaerobic digester, we decided to investigate whether both problems could be (feasibly and economically) addressed by a common solution, (such as dosing of iron solutions to precipitate both sulfide and phosphate), or by using separate approaches.Laboratory results showed that, the hydrogen sulfide emission in digesters could be effectively and economically controlled by the addition of iron dosing. Slightly higher than the theoretical value of 1.5 mol of FeCl 3 was required to precipitate 1 mol of dissolved sulfide inside the digester.Due to the high concentration of PO 4 3-in the digested sludge liquor, significantly higher iron is required for struvite precipitation. Iron dosing did not appear an economic solution for struvite control via iron phosphate formation. By taking advantage of the natural tendency of struvite formation in the digester liquid, it is possible to reduce the risk of struvite precipitation in and around the sludge-dewatering centrifuge by increasing the pH to precipitate struvite out before passing through the centrifuge. However, as the Mg 2+ /PO 4 3-molar ratio in digested sludge was low, by increasing the pH alone (using NaOH) the precipitation of PO 4 3-was limited by the amount of cations (Ca 2+ and Mg 2+ ) available in the sludge. Although this would reduce struvite precipitation in the centrifuge, it could not significantly reduce PO 4 3-recycling back to the plant. For long-term operation, maximum PO 4 3-reduction should be the ultimate aim to minimise PO 4 3-accumulation in the plant. Magnesium hydroxide liquid (MHL) was found to be the most costeffective chemical to achieve this goal. It enhanced struvite precipitation from both, digested sludge and centrate to the point where more than 95% PO 4 3-reduction in the digested sludge was achieved.

The current paper describes a novel passive aeration simultaneous nitrification and denitrification (PASND) zeolite amended biofilm reactor that removes organic carbon and nitrogen from wastewater with low-energy consumption. Next to the ammonium oxidizing bacteria (AOB), this reactor contained naturally enriched glycogen accumulating organisms (GAOs) and zeolite powder to initially adsorb BOD (acetate) and ammonium (NH4+-N) from synthetic wastewater under anaerobic conditions. Draining of the treated wastewater exposed the biofilm directly to air enabling low-energy oxygen supply by passive aeration. This allowed the adsorbed ammonium to be oxidized by the AOB and the produced nitrite and nitrate to be reduced simultaneously by the GAOs using the adsorbed BOD (stored as PHAs) as carbon source. Overall, with an operation mode of 1 h anaerobic and 4 h aerobic phase, the nutrient removal efficiency after single treatment was about 94.3% for BOD and 72.2% for nitrogen (NH4+-N). As high-energy aeration of the bulk solution for oxygen supply is completely avoided, the energy requirement of the proposed PASND biofilm reactor can be theoretically cut down to more than 50% compared to the traditional activated sludge process.