Laboratory-scale investigation of the decentralised anaerobic co-digestion of blackwater and food waste for a tourism facility

The waste management issues that arise from the increasing waste loads on the environment through tourism are an issue of concern considering an expanding industry, and the increasing popularity of ecotourism. Medium to large scale tourism operators are ideally suited to the implementation of decentralised waste management initiatives, designed not only to stabilise the waste but also allow for recovery of resources for reuse locally. Anaerobic digestion is rarely contemplated in small scale applications such as remote tourist destinations. This is due to a perception that such systems are difficult to control and are susceptible to the flow disturbances characteristically experienced by small scale systems, including occasional high loads and seasonal variations, experienced in tourist applications. However, anaerobic digestion has the potential to provide green energy in the form of methane, a sanitised effluent suitable for reuse and a solid residue suitable as a soil amendment. Anaerobic digestion is most suitable for high strength wastes. Source separated blackwater can be effectively treated by anaerobic digestion, however a blackwater stream is relatively dilute as a feedstock for anaerobic digestion even after isolating it from the diluting effect of greywater. This thesis proposes that supplementing blackwater with food waste increases the viability of an anaerobic system by increasing methane yield and by providing a carbon source for biological nutrient removal, with minimal impact on the quality of the treated effluent. This thesis examines how a two-stage, anaerobic co-digestion system for treating a combined blackwater and food waste stream performs under varying organic loads and how well such a system inactivates human pathogens. To perform this investigation, a laboratory scale, two-stage anaerobic co-digestion system was constructed and operated semi-continuously over a 608 day period under low (0%w/w food waste), medium (5%w/w food waste) and high (25%w/w food waste) organic loading rates (OLRs) (1, 1.5 and 3kgCOD.m-3.d-1 respectively). Throughout these experiments, the system exhibited susceptibility to feed OLR as whilst methane yield increased to 78% with the addition of 5%w/w food waste with no decrease in effluent quality, under the highest OLR, methane yield decreased to 42% and the soluble COD in the final effluent increased by 425% to 25g.L-1. Simulation of the system using the Anaerobic Digestion Model No. 1 (ADM1) to investigate system dynamics, kinetics and substrate characteristics indicated that the co-digestion of food waste with blackwater reduces the system hydrolysis rate whilst at the same time increasing the ultimate methane yield of the system. Analysis of the methanogenic kinetics revealed a good system/model correlation and that hydrogen utilising parameters can be estimated with relatively high confidence using methane data. The maximum uptake rate for hydrogen (km_H2) determined for the system of 120 (±15) kgS kgX-1.d-1 and the half saturation rate constant for hydrogen (Ks_H2) of 7x10-5 (±7x10-5) kgS.m-3 are similar to the values for these parameters set into the ADM1, even though hydrogen utilising parameters have not previously been estimated in mixed culture systems. Intensive analysis of indicator pathogen organism inactivation (E. coli, Cl. perfringens and somatic bacteriophage) in the system over a three month period indicated that whilst the thermophilic acidogenic reactor displayed some impact on pathogen counts (average E .coli removal of 105.7cfu per mL and average somatic bacteriophage removal of 103pfu per 100mL), the mesophilic methanogenic reactor had minimal impact on Cl. perfringens and somatic bacteriophage and in the case of E. coli encouraged regrowth. Final membrane filtration as tested by off-line membrane filtration analysis was able to fully remove pathogens and produced effluent that met the microbiological criteria for Queensland Water Recycling Guidelines for Class A+ recycled water. Variations in the OLR had no significant impact on the overall pathogen removal rates from the system. The effluent of the acidogenic reactor was assessed as a carbon source for denitrification as compared to more conventional external carbon sources. The specific denitrification rate of 0.1gNO3-N.gVS-1.d-1 achieved with acidogenic effluent matched that achieved with acetate and was superior to the rate achieved with methanol and butyrate. Overall, the outcomes from this thesis indicate that anaerobic digestion has strong potential for treatment of tourist wastewater in terms of robustness, process stability, energy generation, human pathogen inactivation and provision of an internal carbon source for BNR that lend itself well to a remote or decentralised application

Fishery Science : its methods and applications/ Rounsefell

xii, 444 hal.: ill.; 23 cm