Study of food waste degradation in a simulated septic tank.

Septic systems are typically designed to treat domestic wastewater from households without access to centralized facilities. The installation of a food waste disposer (FWD) may increase the discharge of food waste (FW) into the wastewater; therefore, the installation of a FWD is discouraged in households that have a septic system. This study was conducted to determine how a typical dose of FW from a FWD can affect the performance of a septic system in terms of sewage treatment and solids accumulation. A 20-L control tank was compared with an experiment tank to which FW was added, increasing the amount of total suspended solids (TSS) by 31.3% and total chemical oxygen demands by 46.3% for a period of 110 days. Although the influent water quality changed dramatically, the effluent from the experiment tank had a substantially lower percentage increase in water quality parameters compared with the effluent from the control. It was found that in the experiment tank, 75.8% of FW TSS was degraded, whereas only 36.7% of sewage TSS was degraded, and that 18.8% of FW TSS and 44.9% of sewage TSS accumulated in the experiment tank. The addition of FW increased the scum accumulation, even though the dry matter of the scum layer was much less in quantity than the sludge layer. It also increased the lipid content in the sludge. The increase in the scum layer was mainly due to the increase in protein from the addition of the FW. Overall, compared with sewage TSS, FW TSS tends to be more biodegradable, which indicates that the impact on pumping frequency from adding FW will be insignificant.

Microbial communities in co-digestion of food wastes and wastewater biosolids.

The effect of food waste (FW) co-digestion with wastewater biosolids (WWB) on microbial communities was investigated through running thirteen lab-scale digesters for 100 days at different operational conditions i.e. organic loading rates (2 and 4 kgCOD/m3·day), feed types (WWB and FW), and FW content (10%, 90%, 100%). Compared with mono-digestion of WWB, FW co-digestion enhanced biogas production by 13% and COD degradation rates by up to 101%. Among fermentative bacteria/acetogens, Syntrophomonas was the dominant genus in FW digesters in contrast to the dominance of Clostridium in WWB digesters. The predominant methanogen was Methanosarcina in FW digesters in contrast to Methanosaeta in WWB digesters. COD degradation rates and methane yields were well correlated with Bacteroidetes population. Methane production rate was well correlated with Clostridium for FW digesters, with syntrophs for WWB digesters, and with aceticlastic methanogens for both digesters. Synergism was associated with hydrolytic bacteria, Clostridium, Syntrophomonas, syntrophs, Methanosarcina, and Methanobacterium.

Flocculent Settling of Food Wastes.

This study evaluated the flocculent settling in water and municipal wastewater (MWW) in a 10.6 ft deep column. A total of eight runs at three different testing conditions involving MWW alone, food waste (FW) alone, and FW in MWW (FW+MWW) were conducted. Total suspended solid (TSS), total BOD (TBOD), total COD (TCOD), total nitrogen (TN), and total phosphorous (TP) removal efficiencies after 3 hours of settling were 62%, 46%, 49%, 46% and 62% for FW, and 50%, 43%, 39%, 37% and 24% for MWW. Removal efficiencies of particulate COD (PCOD) and particulate BOD (PBOD) at the lowest surface overflow rate (SOR) of 1.1 m3/m2/hr corresponding to the longest settling time of 3 hours were 59% and 64% for FW, and 65% and 70% for FW with MWW samples. On the other hand, no significant variation between FW and FW with MWW was observed for PN removal after 3 hours of settling.