Maazuza Othman

Removal of ammonium and phosphate from the supernatant of anaerobically digested waste activated sludge by chemical precipitation

The removal of ammonium (NH(4)(+)) and phosphate (PO(4)(3-)) from supernatant of anaerobic digestion by magnesium ammonium phosphate (MAP) formation was studied. To be able to find out the loss of NH(4)(+) by its transformation to NH(3), rates of NH(4)(+) removal by aeration and by MAP formation combined with aeration were compared. NH(4)(+) removal by aeration was found to be insignificant. The kinetics of MAP formation was fast. The removal rate of NH(4)(+) and Mg(2+) was the smallest and the largest, respectively based on rate constants calculated. The removal of NH(4)(+) showed sensitivity to Mg(2+) and PO(4)(3-) concentrations and controlled the purity of MAP precipitate. The removal of PO(4)(3-) was found to be sensitive to mainly Mg(2+) ion. These results also indicated that as the supernatant solution became more saturated in terms of MAP forming ions, the effect of pH increase became insignificant in the removal of ions from the solution.

Anaerobic co-digestion of municipal food waste and sewage sludge: A comparative life cycle assessment in the context of a waste service provision

This study used life cycle assessment to evaluate the environmental impact of anaerobic co-digestion (AcoD) and compared it against the current waste management system in two case study areas. Results indicated AcoD to have less environmental impact for all categories modelled excluding human toxicity, despite the need to collect and pre-treat food waste separately. Uncertainty modelling confirmed that AcoD has a 100% likelihood of a smaller global warming potential, and for acidification, eutrophication and fossil fuel depletion AcoD carried a greater than 85% confidence of inducing a lesser impact than the current waste service.

The use of laboratory scale reactors to predict sensitivity to changes in operating conditions for full-scale anaerobic digestion treating municipal sewage sludge.

Anaerobic digestion of sewage sludge is highly complex and prone to inhibition, which can cause major issues for digester operators. The result is that there have been numerous investigations into changes in operational conditions, however to date all have focused on the qualitative sensitivities, neglecting the quantitative. This study therefore aimed to determine the quantitative sensitivities by using factorial design of experiments and small semi continuous reactors. Analysis showed total and volatile solids removals are chiefly influenced by retention time, with 79% and 59% of the observed results being attributed to retention time respectively, whereas biogas was mainly influenced by loading rate, 38%, and temperature, 22%. Notably the regression model fitted to the experimental data predicted full-scale performance with a high level of precision, indicating that small reactors are subject to the same sensitivity of full-scale digesters and thus can be used to predict changes loading, retention time, and temperature.

Energy and time modelling of kerbside waste collection: Changes incurred when adding source separated food waste

The collection of source separated kerbside municipal FW (SSFW) is being incentivised in Australia, however such a collection is likely to increase the fuel and time a collection truck fleet requires. Therefore, waste managers need to determine whether the incentives outweigh the cost. With literature scarcely describing the magnitude of increase, and local parameters playing a crucial role in accurately modelling kerbside collection; this paper develops a new general mathematical model that predicts the energy and time requirements of a collection regime whilst incorporating the unique variables of different jurisdictions. The model, Municipal solid waste collect (MSW-Collect), is validated and shown to be more accurate at predicting fuel consumption and trucks required than other common collection models. When predicting changes incurred for five different SSFW collection scenarios, results show that SSFW scenarios require an increase in fuel ranging from 1.38% to 57.59%. There is also a need for additional trucks across most SSFW scenarios tested. All SSFW scenarios are ranked and analysed in regards to fuel consumption; sensitivity analysis is conducted to test key assumptions.

Anaerobic Codigestion of Municipal Wastewater Treatment Plant Sludge with Food Waste: A Case Study

The aim of this study was to assess the effects of the codigestion of food manufacturing and processing wastes (FW) with sewage sludge (SS), that is, municipal wastewater treatment plant primary sludge and waste activated sludge. Bench scale mesophilic anaerobic reactors were fed intermittently with varying ratio of SS and FW and operated at a hydraulic retention time of 20 days and organic loading of 2.0 kg TS/m3·d. The specific biogas production (SBP) increased by 25% to 50% with the addition of 1%–5% FW to SS which is significantly higher than the SBP from SS of 284 ± 9.7 mLN/g VS added. Although the TS, VS, and tCOD removal slightly increased, the biogas yield and methane content improved significantly and no inhibitory effects were observed as indicated by the stable pH throughout the experiment. Metal screening of the digestate suggested the biosolids meet the guidelines for use as a soil conditioner. Batch biochemical methane potential tests at different ratios of SS : FW were used to determine the optimum ratio using surface model analysis. The results showed that up to 47-48% FW can be codigested with SS. Overall these results confirm that codigestion has great potential in improving the methane yield of SS.

Life cycle assessment to compare the environmental impact of seven contemporary food waste management systems

Municipal food waste (FW) represents 35-45% of household residual waste in Australia, with the nation generating 1.6Tg annually. It is estimated that 91% of this FW ends up in landfill. This study used life cycle assessment to determine and compare the environmental impact of seven contemporary FW management systems for two real-life jurisdictions; incorporating the complete waste service and expanding the system to include inert and garden waste. Although, no system exhibited a best ranking across all impact categories, FW digestion based systems were all revealed to have a lower global warming potential than composting and landfilling systems. Mechanical biological treatment, anaerobic co-digestion, and home composting all demonstrated the lowest environmental impacts for two or more of the environmental impact categories assessed. The assessment included market and technological specific variables and uncertainties providing a framework for robust decision making at a municipality level.

Bioethanol potential of Eucalyptus obliqua sawdust using gamma-valerolactone fractionation

Optimisation of conditions for gamma-valerolactone (GVL) pretreatment of Australian eucalyptus sawdust for high cellulose biomass and bioethanol production was demonstrated. Pretreatment parameters investigated included GVL concentrations of 35-50% w/w, temperatures of 120-180 °C and reaction durations of 0.5-2.0 h. Optimum conditions were determined using the response surface method (RSM) and central composite face-centred design. Cellulose content increased from 39.9% to a maximum of 89.3% w/w using treatments with 50% GVL at 156 °C for 0.5 h. Temperature had the most significant effect (RSM p < .05) on cellulose content of residual biomass and reducing operational duration of < 0.5 h may be viable according to RSM. PSSF fermentations of optimised pretreated eucalyptus sawdust produced up to 94% theoretical ethanol yield, which corresponded to approximately 181 kg of ethanol per dry ton of eucalyptus sawdust. The compositions of both the residual biomass and pretreatment liquors show that GVL pretreatment is a promising solvent for lignocellulosic biorefining.

Alkali Pretreatment and Enzymatic Hydrolysis of Australian Timber Mill Sawdust for Biofuel Production

This study investigated the potential use of alkali pretreatment of sawdust from Australian timber mills to produce bioethanol. Sawdust was treated using 3–10% w/w NaOH at temperatures of 60, 121, and −20°C. Two pathways of production were trialled to see the impact on the bioethanol potential, enzymatic hydrolysis for glucose production, and simultaneous saccharification and fermentation (SSF) for ethanol production. The maximum yields obtained were at 121°C and −20°C using 7% NaOH, with 29.3% and 30.6% ethanol yields after 0.5 and 24 hr, respectively, these treatments yielded 233% and 137% increase from the 60°C counter parts. A notable trend of increased ethanol yields with increased NaOH concentration was observed for samples treated at 60°C; for example, samples treated using 10% NaOH produced 1.92–2.07 times more than those treated using 3% NaOH. FTIR analysis showed reduction in crystallinity correlating with increased ethanol yields with the largest reduction in crystallinity in the sample treated at −20°C for 24 hr with 7% NaOH.

Anaerobic digestion/co-digestion kinetic potentials of different agro-industrial wastes: A comparative batch study for C/N optimisation

Anaerobic digestion (AD) of different agro-industrial wastes and their co-digestion potential has been exhaustively studied in this research. It explores variation of feedstock characteristics such as biodegradability and methane potential during AD and anaerobic co-digestion (ACoD) of chicken litter (CL) with yoghurt whey (YW), organic fraction of municipal solid waste (OFMSW), hay grass (HG) and wheat straw (WS) under mesophilic conditions. Comparative performance was made at different loading concentrations (2%, 3% and 4% VS) with 1:2g/g VS of substrate to inoculum and carrying C/N ratio. Among different kinetic models, the AD of single substrates showed better fit to the modified Gompertz model (R2: 0.93-0.997) indicating variation in lag phase and methane production rate depend on the substrate characteristics. During ACoD, the methane yield improved by 9-85% through the addition of two, three or four substrates due to the synergistic effect asa result of increased biodegradability and optimum conditions (such asC/N ratio). A surface (optimisation) model indicated that maximum methane production can be achieved by blending chicken litter (30-35%) and a (65-70%) mixture of yoghurt whey, hay and wheat straw with aC/N ratio of (26-27.5).

Application of Victorian brown coal for removal of ammonium and organics from wastewater

ABSTRACT Brown coal is a relatively abundant and low-cost material, which has been used as an effective ion-exchanger to remove ammonium from wastewater. In this study, the influences of pH, ammonium concentration and brown coal dose were investigated for removal of ammonium content from synthetic wastewater. Raw brown coal (RBC) treated with base solution has superior ammonium removal efficiency compared to RBC, which was due to chemical alterations and thus greater attachment of ammonium molecules to base-washed brown coal (BWBC), confirmed by Fourier transform infra-red spectroscopy. Scanning electron microscopy-electron diffraction scattering has identified the augmented sodium content in BWBC, which was subsequently replaced with nitrogen upon wastewater treatment. Crystallographic analysis showed a higher crystallinity formed in BWBC compared to RBC, which was likely due to formation of sodium salt crystals during NaOH treatment. Fitting batch experimental results to adsorption kinetic models suggested that the removal of ammonium was mainly governed by the reaction process rather than the physical diffusion mechanism. Both kinetic and isotherm studies confirmed higher adsorption capacity for BWBC compared to RBC. RBC in column mode was also experimented with to show organics removal from a secondary effluent. A comparatively lower removal of organics was obtained due to inability of charge neutralization as both brown coal and organics are positively charged.