In this study, the optimum mixing ratio of food waste (FW) and livestock manure (LM) was investigated to improve the methane yield efficiency and prohibit the inhibition factors (organic loading rate and NH₄⁺) from inhibiting the anaerobic co-digestion of FW and LM under mesophilic and thermophilic conditions. The research involved the following: (I) the analysis of the characteristics of FW and LM, (II) the evaluation of the potential and toxicity of the anaerobic digestion of I have confirmed that there is no problem. FW and LM using the biochemical methane potential (BMP) and anaerobic toxicity assay (ATA) tests, (III) the evaluation of the anaerobic co-digestion of FW and LM using the BMP test, and (IV) the evaluation of the optimum mixing ratio using mathematical modeling. The characteristics of FW and LM were analyzed to evaluate the theoretical methane potential and inhibition factor. The BMP test was carried out to evaluate the concentration of the biodegradable organic matter, biogas production rate, and methane yield. The ATA test was carried out to evaluate the impact of the inhibition concentration. Ultimately, mathematical models, such as a first-order reaction and a modified Gompertz model, were implemented to evaluate the optimum mixing ratio for the anaerobic co-digestion of FW and LM. FW had a higher concentration of degradable organic matter than LM. The initial operational parameters of the anaerobic digestion were determined to be appropriate at an organic matter concentration of less than 2.5 g/L and a TN concentration of 2,000 mg/L. In conclusion, as a result of evaluation through mathematical models, it was determined that anaerobic microorganisms were more sensitive to inhibitory factors under the thermophilic condition than under the mesophilic condition, and the optimum mixing ratio of FW to LM was 5:1 (vol:vol) based on kinetic results (k: 0.080; B_u: 0.23 L CH₄/g VS_added; P: 100.84 mL; R_m: 10.23 mL/day; λ: 1.44 days).

Anaerobic digestion of Thermally Hydrolyzed Wasted Sludge (THWS) with high strength ammonia was evaluated through batch and two-phase Upflow Anaerobic Sludge Blanket (UASB) reactors with two kinds of anaerobic microbial types (suspended and granular). In the batch test, biogas yield and gas production rate increased as microbial concentration increased for the wastewaters with a high ammonia concentration of 0.8 g FA/L. Also, the lag time and finishing time of gas production could be shortened by applying higher microbial concentrations. The granular sludge presented a higher biogas yield, shorter lag time and shorter finishing time of gas production when compared with suspended sludge. The comparative reactor operation using suspended sludge and granular sludge demonstrated that the granular sludge had more competitive advantages for the biogas production from THWS at a high ammonia concentration of 9.2 g NH ₄ ⁺ /L. Therefore, the application of granular sludge could be more appropriate for the anaerobic treatment of wastewater containing high strength ammonia since the granular sludge can have a higher resistance to toxicity and maintain a higher microbial concentration.

In this study, the characteristics partial nitrifying biomass in the Sequencing Batch Reactor (SBR) for aerobic granulation was investigated based on experiments and simulation modeling. The reactor operation was carried out at high concentration of ammonium (200~850 mg N/L) which favored Ammonia-Oxidizing Bacteria (AOB) growth over Nitrite-Oxidizing Bacteria (NOB) growth. In partial nitrifying granulation, both Free Ammonia (FA) and Free Nitrous Acid (FNA) simultaneously influenced the activity of NOB much more than that of AOB. According to the simulation results, thE Dissolved Oxygen (DO) concentration and oxygen affinity affect the growth competition and can influence the species that are predominant in the reactor. Both AOB and NOB can have growth potential under toxicants (FA and FNA) inhibition and limited oxygen condition. The AOB growth forms inner part of granule’s biofilm, but the NOB growth does not engage in the formation of granules.

Livestock manure wastewater is a representative high-strength wastewater characterized by high concentrations of organic matter and ammonia, which can hinder stable biological treatment and nitrification. In this study, an immersed membrane bioreactor (MBR) equipped with an end-free hollow fiber membrane was operated to evaluate the effects of mixed liquor suspended solids (MLSS) concentration on nitrification and membrane filtration performance during livestock manure wastewater treatment. The influent wastewater had average concentrations of pH 8.6, CODcr 24,476 mg/L, T-N 2,593mg/L, NH3-N 1,979 mg/L, TS 21,851 mg/L, and TSS 12,519mg/L. The reactor was operated by stepwise increases in MLSS from approximately 4,050 to 18,872 mg/L. As MLSS increased, nitrification efficiency improved from 7.7% at 4,050mg/L to 70.3% at 15,828 mg/L, but slightly decreased to 66.2% at 18,872mg/L. This result indicates that increasing biomass concentration promoted nitrifier retention and nitrification, whereas excessively high MLSS likely limited oxygen transfer and reduced nitrification performance. Transmembrane pressure (TMP) increased gradually with increasing MLSS, and a marked acceleration in the rise of TMP was observed above approximately 15,000mg/L, indicating intensified membrane fouling under high-solids conditions. Under the MLSS condition of about 15,000 mg/L, the TMP increase rate of the end-free hollow fiber membrane was 0.05 kPa/d, which was lower than those reported at comparable operating points in previous MBR studies. These results suggest that an MLSS level of approximately 15,000mg/L can be considered an appropriate operating condition for balancing nitrification efficiency and membrane filtration stability, and that the end-free hollow fiber configuration may provide a useful structural option for mitigating fouling in high-strength livestock manure wastewater treatment.