Qianqian Lang

Combined effect of crude fat content and initial substrate concentration on batch anaerobic digestion characteristics of food waste

The mesophilic anaerobic digestion (AD) characteristics of food waste (FW) with different crude fat (CF) contents and four initial substrate concentrations (4, 6, 8, and 10gVS/L) were investigated. The maximum methane yields of FW with CF contents of 15%, 20%, 25%, 30%, and 35% were 565.0, 580.2, 606.0, 630.2 and 573.0mLCH4/gVSadded, respectively. An acidification trend with a drop in pH (<6.80) and increase in the volatile fatty acids/total inorganic carbon (VFAs/TIC) ratio (>0.4) were found for CF contents of 30% (10gVS/L) and 35% (8 and 10gVS/L). A 35% CF content in FW led to decrease in the first-order degradation constant of approximately by 40%. The modified Gompertz model showed that the lag phase (λ) was prolonged from 0.4 to 7.1days when the CF content in FW and initial substrate concentration were increased to 35% and 10gVS/L.

Effect of hydrothermal carbonization on migration and environmental risk of heavy metals in sewage sludge during pyrolysis

The heavy metals distribution during hydrothermal carbonization (HTC) of sewage sludge, and pyrolysis of the resultant hydrochar was investigated and compared with raw sludge pyrolysis. The results showed that HTC reduced exchangeable/acid-soluble and reducible fraction of heavy metals and lowered the potential risk of heavy metals in sewage sludge. The pyrolysis favored the transformation of extracted/mobile fraction of heavy metals to residual form especially at high temperature, immobilizing heavy metals in the chars. Compared to the chars from raw sludge pyrolysis, the chars derived from hydrochar pyrolysis was more alkaline and had lower risk and less leachable heavy metals, indicating that pyrolysis imposed more positive effect on immobilization of heavy metals for the hydrochar than for sewage sludge. The present study demonstrated that HTC is a promising pretreatment prior to pyrolysis from the perspective of immobilization of heavy metals in sewage sludge.

Performance evaluation of a novel anaerobic digestion operation process for treating high-solids content chicken manure: Effect of reduction of the hydraulic retention time at a constant organic loading rate

A novel feeding strategy was adopted in this study and the effect of reduction in hydraulic retention time (HRT) on the anaerobic digestion of chicken manure (CM) with a constant organic loading rate of 6.0gVS/L/d was investigated. The lab-scale CSTR was operated at 38°C and HRTCM was reduced from 52days to 5days. At HRTCM of 20-45days, the reactor was relatively stable in terms of the volumetric biogas production rates and specific biogas production (SBP), which were 2.2-2.4L/L/d and 338.3-418.7mL/gVSadded, respectively. However, process instability and VFA accumulation occurred when the HRTCM was reduced to 10days due to excess microbes washout. The reduction in HRTCM to 5days caused SBP to decrease to 198.7mL/gVSadded and the acetic acid content to exceed 6000mg/L. The biomass balance model showed that the biomass concentration at HRTCM of 20-52days (0.473-0.615gVSS/L) was notably higher than that at HRTCM of 5-10days (0.173gVSS/L).

Co-hydrothermal carbonization of corn stalk and swine manure: Combustion behavior of hydrochar by thermogravimetric analysis

The combustion behavior of the hydrochar from co-hydrothermal carbonization (HTC) of corn stalk (CS) and swine manure (SM) was thermogravimetrically investigated. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were used for kinetic analysis, and the thermodynamic parameters were determined. Results showed that HTC decreased the combustion property and stability of SM, while co-HTC with CS significantly improved the combustion performance of the hydrochar including the increased ignition temperature and decreased burnout temperature. HTC of SM decreased the average activation energy (Ea) value from 140.40 and 137.31 KJ/mol to 124.40 and 120.17 KJ/mol by FWO and KAS, respectively, and increasing proportion of CS during co-HTC increased the Ea value of the hydrochar to 141.53-171.23 and 138.35-169.66 KJ/mol, respectively. The thermodynamic parameters confirmed the enhanced combustion reactivity of the hydrochar from co-HTC of CS and SM. These findings demonstrated that co-HTC with CS benefited the hydrochar production from SM with improved combustion performance.

Hydrochar supported bimetallic Ni–Fe nanocatalysts with tailored composition, size and shape for improved biomass steam reforming performance

Multicomponent nickel–iron alloy nanoparticles supported on hydrochar were synthesized by a facile one-step hydrothermal strategy. Spinel nickel ferrite (NiFe2O4) with a small crystalline size around 10 nm was uniformly dispersed on a bimetallic catalyst. The roles of the Ni/Fe doping concentration and calcination temperature in tailoring the phase, morphology and size of the Ni–Fe alloy nanoparticles were investigated. To probe the catalytic abilities of the prepared bimetallic catalysts, a two-stage reaction system was applied for steam gasification of sewage sludge. Compared to monometallic nickel nanoparticles, the synthesized bimetallic catalyst, especially Ni0.25Fe0.25/HC calcined at 700 °C, showed excellent dispersibility of the Ni–Fe alloy NPs and exhibited a strong metal–support interaction, which allowed for better suppression of carbon deposition and nanoparticle agglomeration in the reforming process. The best catalytic performance resulted in a promoted hydrogen selectivity of 113.7 g H2 per kg sludge with a low tar yield of 2.3 mg g−1 under mild gasification conditions. These shape- and size-modulated nanocatalysts harbor promising potential for their application as a highly efficient catalyst for hydrogen production via steam gasification of sewage sludge.

Co-hydrothermal carbonization of lignocellulosic biomass and swine manure: Hydrochar properties and heavy metal transformation behavior

Co-hydrothermal carbonization (HTC) of lignocellulosic biomass and swine manure (SM) was conducted, and the hydrochar properties and transformation behavior of heavy metals (HMs) were investigated in this study. The results showed that co-HTC with lignocellulosic biomass promoted the dehydration of SM and enhanced the aromatization of the hydrochar. Compared to the hydrochar from SM, the carbon content, higher heating value and energy yield of the hydrochar from co-HTC were significantly increased, reaching the maximum of 57.05%, 24.20 kJ/kg and 80.17%, respectively. Significant synergy occurred between lignocellulosic biomass and SM during co-HTC and different lignocellulosic biomass exhibited similar influence on the synergy. Additionally, the concentration and bioavailability of HMs in the hydrochar from co-HTC were decreased in comparison to SM. These findings suggested that co-HTC with lignocellulosic biomass offered an effective approach to convert SM into clean solid fuel with remarkably improved fuel properties.