George Nakhla

Biochemical methane potential (BMP) of food waste and primary sludge: Influence of inoculum pre-incubation and inoculum source

Biochemical methane potential tests were conducted to evaluate the effect of using a blank versus a pre-incubated inoculum in digestion of primary sludge at different waste to inoculum ratios (S/X). In addition, this study explored the influence of using two different anaerobic inoculum sources on the digestion of food waste: digested sludge from a municipal wastewater treatment plant and from a digester treating the organic fraction of municipal solid wastes. The results revealed that although there was no significant difference in methane yield (on average 114mLCH(4)/g TCOD(sub)) or biodegradability (on average 28.3%) of primary sludge using pre-incubated or non-incubated inocula, the maximum methane production rates using non-incubated inoculum were higher than those using pre-incubated inoculum at all S/X ratios. Moreover, interestingly the inoculum from an anaerobic digester treating municipal wastewater sludge was superior over the inoculum from anaerobic digester treating food waste in digesting food waste.

Techno-economic evaluation of ultrasound and thermal pretreatments for enhanced anaerobic digestion of municipal waste activated sludge

To enhance the anaerobic digestion of municipal waste-activated sludge (WAS), ultrasound, thermal, and ultrasound+thermal (combined) pretreatments were conducted using three ultrasound specific energy inputs (1000, 5000, and 10,000 kJ/kg TSS) and three thermal pretreatment temperatures (50, 70 and 90°C). Prior to anaerobic digestion, combined pretreatments significantly improved volatile suspended solid (VSS) reduction by 29-38%. The largest increase in methane production (30%) was observed after 30 min of 90°C pretreatment followed by 10,000 kJ/kg TSS ultrasound pretreatment. Combined pretreatments improved the dimethyl sulfide (DMS) removal efficiency by 42-72% but did not show any further improvement in hydrogen sulfide (H(2)S) removal when compared with ultrasound and thermal pretreatments alone. Economic analysis showed that combined pretreatments with 1000 kJ/kg TSS specific energy and differing thermal pretreatments (50-90°C) can reduce operating costs by

Comparative assessment of single-stage and two-stage anaerobic digestion for the treatment of thin stillage

44-66/ton dry solid when compared to conventional anaerobic digestion without pretreatments.

Optimization of biological hydrogen production for anaerobic co-digestion of food waste and wastewater biosolids.

A comparative evaluation of single-stage and two-stage anaerobic digestion processes for biomethane and biohydrogen production using thin stillage was performed to assess the impact of separating the acidogenic and methanogenic stages on anaerobic digestion. Thin stillage, the main by-product from ethanol production, was characterized by high total chemical oxygen demand (TCOD) of 122 g/L and total volatile fatty acids (TVFAs) of 12 g/L. A maximum methane yield of 0.33 L CH(4)/gCOD(added) (STP) was achieved in the two-stage process while a single-stage process achieved a maximum yield of only 0.26 L CH(4)/gCOD(added) (STP). The separation of acidification stage increased the TVFAs to TCOD ratio from 10% in the raw thin stillage to 54% due to the conversion of carbohydrates into hydrogen and VFAs. Comparison of the two processes based on energy outcome revealed that an increase of 18.5% in the total energy yield was achieved using two-stage anaerobic digestion.

Simultaneous nitrification–denitrification in slow sand filters

Batch anaerobic co-digestion studies were conducted using 21 mixtures (M1-M21) of food waste (FW), primary sludge (PS), and waste activated sludge (WAS) at 37°C and an initial pH of 5.5±0.2. The results showed that co-digestion of FW and sludges had a positive impact on the hydrogen production. The maximum hydrogen yields by co-digestion of FW+PS, FW+WAS, and FW+PS+WAS were achieved at volumetric ratios of 75:25, 75:25, and 80:15:5, respectively, with corresponding optimal COD/N mass ratios of 26, 31 and 30, respectively. Furthermore, the synergistic effect of co-digestion was proven and quantified: the measured hydrogen productions were higher than the sums of the hydrogen productions calculated from each fraction, and the highest percentage increase above the calculated value of 101%, was achieved in the FW+PS+WAS mixture (80:15:5).

Comparative study of the effect of ultrasonication on the anaerobic biodegradability of food waste in single and two-stage systems

While the ability of slow sand filters to remove total suspended solids (SS), turbidity, and organics from wastewaters is well known, this study has demonstrated that they can also achieve simultaneous nitrification-denitrification, producing effluent total Kjedahl nitrogen (TKN) and total nitrogen (TN) concentrations as low as 0.6 and 1.5mg/l, respectively, utilizing particulate and slowly biodegradable COD in the process. The impact of filtration rates in the range of 0.15-0.38m/h, filter depth of 0.5-1.5m, and sand size 0.3-0.5mm on nitrogen removal processes at temperatures of 10-39 degrees C was assessed. Nitrification efficiency, denitrification efficiency, and total nitrogen removal efficiency correlated well with filtration rate and sand size only, with all three parameters inversely proportional to the square root of the aforementioned two process variables. Nitrification exhibited the most sensitivity to filtration rate and sand size. The filters produced effluent with turbidities of 0.1-0.5 NTU, SS concentrations of 3-6mg/l in the fine sand and 6-9mg/l in the coarse sand. Effluent BOD(5) and COD concentrations were mostly in the 0.8-2.6 and 15-34mg/l range, respectively.

Batch anaerobic co-digestion of proteins and carbohydrates.

Five different mesophilic systems were evaluated in this study for the anaerobic treatment of food waste. Systems A and B were one stage methane with unsonicated and sonicated feeds, respectively, while, systems C and D were two-stage hydrogen and methane with unsonicated and sonicated feeds, respectively. System E comprised a novel sonicated biological hydrogen reactor (SBHR) followed by methane reactor. The results showed that sonication inside the reactor in the first stage (system E) showed superior results compared to all other systems. Overall VSS removal efficiencies of 67%, 59%, 51%, 44%, and 36% were achieved in systems E, D, C, B, and A, respectively. Volumetric hydrogen production rates of 4.8, 3.3, and 2.6L H(2)/L(reactor)d were achieved in the SBHR, CSTR with and without sonicated feed, respectively, while, methane production rates of 1.6, 2.1, 2.3, 2.6, and 3.2L CH(4)/L(reactor)d were achieved in systems A-E, respectively.

Impact of ultrasonication of hog manure on anaerobic digestability

Batch anaerobic studies were conducted using five mixtures (M1-M5) of bovine serum albumin (BSA) and starch. The results showed that co-digestion of BSA and starch had a positive impact on the methane production. The highest methane production of 288 mL, the highest methane yield of 360 mL CH(4)/g COD(added), and the highest maximum methane production rate of 62 mL CH(4)/d were achieved for M4 (20% BSA and 80% starch). Most of the particulate proteins (90%) as well as particulate carbohydrates (95%) were degraded in the first 3 days. The hydrolysis coefficients of particulate proteins and particulate carbohydrates ranged from 0.65 to 1.01 d(-1) and from 0.53 to 1.06 d(-1), respectively. The highest methane production was achieved at C:N ratio of 12.8 for M4. For BSA only, propionic acid was the main volatile fatty acid (VFA), while for the starch only, butyric acid was the predominant VFA.

ANAEROBIC TREATABILITY OF HIGH OIL AND GREASE RENDERING WASTEWATER

The efficiency of ultrasonication as a pretreatment method for hog manure prior to anaerobic digestion is evaluated at specific energies of 250-30,000 kJ/kgTS. This study confirmed that COD(solubilisation) from particulates correlated well with the more labor and time intensive degree of disintegration test. The particle size distribution for hog manure was bimodal (0.6-2500 μm), while ultrasonication primarily impacting particles in the 0.6-60 μm range. Hog manure was found to be more amenable to ultrasonication than waste activated sludge, as it took only 3000 kJ/kgTS to cause 15% more solubilization as compared to 25,000 kJ/kgTS for waste activated sludge. Bound protein degradation during sonication was 13.5% at 5000 kJ/kgTS and remained constant thereafter for higher energy input. It was noted that biomass cell rupture occurred at specific energy of 500 kJ/kgTS. An economic evaluation indicated that only a specific energy of 500 kJ/kgTS was economical, with a net energy output valued at

Simultaneous Carbon and Nitrogen Removal in Anoxic-Aerobic Circulating Fluidized Bed Biological Reactor (CFBBR)

4.1/ton of dry solids, due to a 28% increase in methane production.