Mingu Kim

Characterization of typical household food wastes from disposers: Fractionation of constituents and implications for resource recovery at wastewater treatment

Food wastes with typical US food composition were analyzed to characterize different constituents in both particulate and soluble phases i.e., solids, chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD), nitrogen (N), phosphorus (P). Relationships between various pollutants were also investigated using 50 samples. One gram of dry food waste generated 1.21 g COD, 0.58 g BOD5, 0.36 g Total SS, 0.025 g Total N, and 0.013 g Total P. Distribution of constituents between particulate and aqueous phases indicated that 40% of COD and 30% of nitrogen were present in soluble form. Relative mass ratios of COD and nitrogen to solids were three to five times higher in particulates than in aqueous phase. However, COD/N ratios were higher in aqueous form than particulates at 63:1 versus 42:1. Detailed relationships between parameters showed that COD, nitrogen, and phosphorus in particulates are 200%, 3.6%, and 3.5% of the volatile suspended solids.

Synergism of co-digestion of food wastes with municipal wastewater treatment biosolids.

Five semi-continuous flow anaerobic digesters treating a mixture of food waste (FW) and municipal biosolids (primary sludge and thickened wasted activated sludge) at an solids retention time (SRT) of 20 days and different blend ratios i.e. 0, 10%, 20%, 40% by volume with the fifth digester treating only biosolids at the same COD/N ratio as the 40% FW digester were operated to investigate co-digestion performance. Sixty days of steady-state operation at organic loading rates (OLR) of 2.2-3.85kgCOD/m3/d showed that COD removals were higher for the three co-digesters than for the two municipal biosolids digesters i.e. 61-69% versus 47-52%. Specific methane production per influent CODs were 1.3-1.8 folds higher in co-digestion than mono-digestion. The first-order COD degradation kinetic constants for co-digestion were more than double the mono-digestion. Additional methane production through synergism accounted for a minimum of 18-20% of the overall methane production. The estimated non-biodegradable fraction of the FW particulate COD was 7.3%. However, the co-digesters discharged 1.23-1.64 times higher soluble nitrogen than the control.

Operational conditions for successful partial nitrification in a sequencing batch reactor (SBR) based on process kinetics

ABSTRACT The objective of this study is to analyze the factors affecting the performance of partial nitrification in a sequencing batch reactor (SBR) using kinetic models. During the 4-month operation, dissolved oxygen (DO) and influent ammonia concentration were selected as operating variables to evaluate nitrite accumulation. Stable partial nitrification was observed with two conditions, influent ammonia concentration of 190 mg N/L and a DO of 0.6–3.0 mg/L as well as influent ammonia concentration of 100 mg N/L and a DO of 0.15–2.0 mg/L with intermittent aeration. At a DO of 0.6–3.0 mg O2/L and influent ammonia concentration of 90 mg N/L, nitrite-oxidizing bacteria growth was not suppressed. Kinetic parameters were determined or estimated with batch tests and model simulation. The kinetic model predicted the SBR performance well.

Phosphorus fractionation in membrane-assisted biological nutrient removal processes

A comparison between a patented novel membrane bioreactor (NMBR) and conventional University of Cape Town adapted MBR (UMBR) was conducted using two different municipal wastewaters at a total bioreactor hydraulic retention time of 6h and sludge retention time of 10d. Total nitrogen removal efficiencies were 73-80% and 70-77% for the NMBR and UMBR, respectively, with 1-1.7 mgL(-1) lower effluent nitrates in the NMBR. The average effluent P in the NMBR and UMBR were 0.5 and 0.8 mgL(-1), respectively. P uptake by denitrifying phosphate accumulating organisms (DPAO) accounted for 37-40% of the total uptake in both systems and DPAOs were 40% of PAO. Sludge P fractionation substantiated that poly-P content increased from 27-37% to 57-59% of the total phosphorus, with P increasing from around 3% to 6% by weight upon the supplementation of the wastewater volatile fatty acids.

Synergistic Effects of Codigesting Preprocessed Food Waste Slurry

Anaerobic digestion is the most widely used technology to produce biogas such as methane and hydrogen from the decomposition of organic compounds. The effectiveness of the process depends on the stability of the consecutive reactions i.e. hydrolysis, acidification, acetogenesis, and methanogenesis. The process is widely used in sludge treatment for stabilization and production of methane gas. Due to the recent demand of renewable energy, anaerobic digestion has also been used for treating biodegradable wastes; for instance, the organic fraction of municipal solids wastes, wastewater treatment biosolids, and various food and beverage wastes (Arsova, 2010). Particularly, anaerobic digestion of food wastes (FW) is also considered as one of the effective methods of waste management. However, digestion stability can be hampered when FW is used as single substrate due to the high variability of its composition depending on its source (Lacovidou et al., 2012). Thus, the use of FW as co-substrate for municipal sludge digestion has emerged to enhance sludge digestibility, and increase energy generation to facilitate the achievability of energy-neutral wastewater treatment.

Effective partial nitrification of ammonia in a fluidized bed bioreactor

ABSTRACT A lab-scale fluidized bed bioreactor with high-density polyethylene as biofilm carrier media was operated to study partial nitrification (PN) performance with high ammonia concentrations. The system was run at nitrogen loading rates (NLRs) from 1.2 to 4.8 kg N/(m3 d) with empty bed contact time of 2.0 and 2.7 h and four different influent ammonia concentrations of 100, 200, 300 and 400 mg/L. Dissolved oxygen concentration and temperature were maintained around 1.3 mg/L and 35°C, respectively. Stable PN was successfully achieved during the whole period with low effluent NO3-N concentration at less than 15 mg/L, due to effective suppression of nitrite-oxidizing bacteria activity at high concentrations of free ammonia (5.3–27.3 mg N/L) and low alkalinity-to-ammonia ratio. At the NLR of 3.6 kg N/(m3 d), NH4-N conversion and NO2-N accumulation ratios were 57.8% and 53.9%, respectively, which could be further used in the anaerobic ammonium oxidation process (ANAMMOX) as the effluent NO2-N/NH4-N ratio was 1.27.

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.