Shuyan Li

Control of dimethyl sulfide and dimethyl disulfide odors during pig manure composting using nitrogen amendment

Effects of nitrogen electron acceptors on dimethyl sulfide (Me2S) and dimethyl disulfide (Me2SS) odor emission during composting was investigated. The chemicals and doses used included sodium nitrate (NO3- at 10mM, 20mM and 40mM), sodium nitrite (NO2- at 10mM, 20mM and 40mM) and sodium nitrite (10mM, 20mM and 40mM) with hexaammonium heptamolybdate tetrahydrate (HHT). The results showed that the addition of these chemicals restricted the emission of Me2S and Me2SS. The emission reduction effect of NO2- was greater than NO3- at the same dosage. A greater reduction was observed when HHT was also added. With 2mM HHT+40mM NO2- addition, the emission of Me2S and Me2SS was reduced by 92.3% and 82.3%, respectively. Comparison of compost maturity indices for treated and untreated composts indicated that none of the additives adversely affected compost quality. These results indicate that nitrogen chemical addition may provide an efficient method to control sulfur odors during composting.

Solid state anaerobic co-digestion of tomato residues with dairy manure and corn stover for biogas production

Solid-state anaerobic co-digestion of tomato residues with dairy manure and corn stover was conducted at 20% total solids under 35°C for 45days. Results showed digestion of mixed tomato residues with dairy manure and corn stover improved methane yields. The highest VS reduction (46.2%) and methane yield (415.4L/kg VSfeed) were achieved with the ternary mixtures of 33% corn stover, 54% dairy manure, and 13% tomato residues, lead to a 0.5-10.2-fold higher than that of individual feedstocks. Inhibition of volatile fatty acids (VFAs) to biogas production occurred when more than 40% tomato residues were added. The results indicated that ternary mixtures diluted the inhibitors that would otherwise cause inhibition in the digestion of tomato residues as a mono-feedstock.

Effects of mix ratio, moisture content and aeration rate on sulfur odor emissions during pig manure composting

Sulfur compounds in swine manure can cause odor emissions during composting if conditions are not conducive to their rapid oxidation and degradation. In this study, the effects of controllable composting process variables on sulfur odor emissions were investigated. These included pig manure to corn stalk mix ratio (0.7:1, 1.5:1 and 2.2:1dw basis), initial moisture content (60%, 65%, 70% and 75%) and aeration rate (1.0, 2.0, 3.0 and 4.0m(3)m(-3)h(-1)). The compounds measured were carbonyl sulfide, carbon disulfide, hydrogen sulfide, methyl mercaptan, ethyl mercaptan, diethyl sulfide, dimethyl sulfide (Me2S) and dimethyl disulfide (Me2SS). The results showed that total sulfur losses ranged from 3.9% to 18.3% after 26days of composting. Me2S and Me2SS were the primary (>59.61%) sulfur compounds released during this period. After turning, emission rates of both Me2S and Me2SS increased. Emissions of the other six sulfur compounds were low and inconsistent during composting. Within the compost, feedstock mix ratio significantly influenced the concentration of Me2SS, while aeration rate significantly affected Me2S concentration (p<0.05). Moisture content did not have a significant effect on the concentrations of either of these two compounds. Concentrations of sulfur odor compounds were the lowest at the highest aeration rate. Therefore, high aeration rates during the thermophilic phase, especially after turning, are recommended to minimize sulfur odors produced during swine manure composting.

The influences of inoculants from municipal sludge and solid waste on compost stability, maturity and enzyme activities during chicken manure composting

ABSTRACT The aim of this study was to investigate the influence of inoculants on compost stability, maturity and enzyme activities during composting of chicken manure and cornstalk. Two microbial inoculants (originated from aerobic municipal sludge and municipal solid waste, respectively) were used in composting at the rate of 0.3% of initial raw materials (wet weight). No microbial inoculums were added to the control. The experiment was conducted under aerobic conditions for 53 days. The results show that enzyme activity is an important index to comprehensively evaluate the composting stability and maturity. Microbes originated from sludge works best in terms of composting stability and maturity (C:N ratio decreased from 15.5 to 10, and germination index increased to 109%). Microbial inoculums originated from sludge and municipal solid waste extended the time of thermophilic phase for 11 and 7 days, respectively. Microbial inoculums originated from sludge and MSW significantly increased the average of catalase activity (by 15.0% and 12.1%, respectively), urease activity (by 21.5% and 12.2%, respectively) and cellulase activity (by 32.1% and 26.1%, respectively) during composting.

Evaluation of humic substances during co-composting of sewage sludge and corn stalk under different aeration rates

Sewage sludge and corn stalk were co-composted under different aeration rates 0.12 (AR0.12), 0.24 (AR0.24), 0.36 (AR0.36)L·kg-1DMmin-1, respectively. Transformation of humic substance was evaluated by a series of chemical and spectroscopic methods to reveal compost humification. Results showed that aeration rate could significantly affect compost stability and humification process. Humic acid contents in AR0.24 were significantly higher than those in the other two treatments. The final humic acid/fulvic acid ratios in AR0.12, AR0.24 and AR0.36 treatment were 1.0, 1.9 and 0.8, respectively, corresponding to the final E4/E6 of 4.7, 3.2 and 5.5. Moreover, compost in AR0.24 treatment had a high stability degree due to the low C/N atom ratio and high C/H atom ratio. However, it is noteworthy that composting could not significantly affect the structure of HA in a 35-day period. These results indicate that composting with the aeration rate of 0.24L·kg-1DMmin-1 could accelerated the humification process.

Reactor performance and energy analysis of solid state anaerobic co-digestion of dairy manure with corn stover and tomato residues

Anaerobic co-digestion is commonly believed to be benefical for biogas production. However, additional of co-substrates may require additional energy inputs and thus affect the overall energy efficiency of the system. In this study, reactor performance and energy analysis of solid state anaerobic digestion (SS-AD) of tomato residues with dairy manure and corn stover were investigated. Different fractions of tomato residues (0, 20, 40, 60, 80 and 100%, based on volatile solid weight (VS)) were co-digested with dairy manure and corn stover at 15% total solids. Energy analysis based on experimental data was conducted for three scenarios: SS-AD of 100% dairy manure, SS-AD of binary mixture (60% dairy manure and 40% corn stover, VS based), and SS-AD of ternary mixture (36% dairy manure, 24% corn stover, and 40% tomato residues, VS based). For each scenario, the energy requirements for individual process components, including feedstock collection and transportation, feedstock pretreatment, biogas plant operation, digestate processing and handling, and the energy production were examined. Results showed that the addition of 20 and 40% tomato residues increased methane yield compared to that of the dairy manure and corn stover mixture, indicating that the co-digestion could balance nutrients and improve the performance of solid-state anaerobic digestion. The energy required for heating substrates had the dominant effect on the total energy consumption. The highest volatile solids (VS) reduction (57.0%), methane yield (379.1 L/kg VSfeed), and net energy production were achieved with the mixture of 24% corn stover, 36% dairy manure, and 40% tomato residues. Thus, the extra energy input for adding tomato residues for co-digestion could be compensated by the increase of methane yield.

Effect of spent mushroom substrate as a bulking agent on gaseous emissions and compost quality during pig manure composting

The aim of this study was to investigate the gaseous emissions (CH4, N2O, and NH3) and compost quality during the pig manure composting by adding spent mushroom substrate (SMS) as a bulking agent. The control treatment was also studied using corn stalk (CS) as a bulking agent. The experiment was conducted in a pilot scale composting reactor under aerobic condition with the initial C/N ratio of 20. Results showed that bulking agents significantly affected gaseous emissions and compost quality. Using SMS as a bulking agent improved composting efficiency by shortening the time for maturity. SMS increased germination index and humic acid of the final compost (by 13.44 and 41.94%, respectively) compared with CS. Furthermore, composting with SMS as a bulking agent could reduce nitrogen loss, NH3, and N2O emissions (by 13.57, 35.56, and 46.48%, respectively) compared with the control. SMS slightly increased CH4 emission about 1.1 times of the CS. However, a 33.95% decrease in the global warming potential of CH4 and N2O was obtained by adding SMS treatment. These results indicate that SMS is a favorable bulking agent for reducing gaseous emissions and increasing compost quality.

Effect of inoculum and substrate/inoculum ratio on the performance and methanogenic archaeal community structure in solid state anaerobic co-digestion of tomato residues with dairy manure and corn stover

Effects of methanogenic community of inoculum (liquid anaerobic digestion effluent (L-AD effluent), waste activated sludge (WAS), and anaerobic granular sludge (AGS)) and substrate/inoculum ratio (S/I) on reactor performance in solid state anaerobic digestion (SS-AD) were investigated. L-AD effluent, which can provide sufficient microbes and enough buffering capacity to the reactor at an S/I ratio of 6, was found to quickly initiate SS-AD processes. The highest methane production was obtained in reactor inoculated with WAS at an S/I ratio of 2. Higher volatile fatty acids and total ammonia nitrogen concentrations were found when AGS was used as inoculum, which led to a low methane production. Methanosaetaceae, Methanosaetaceae, and Methanosaetaceae together with Methanobacteriaceae were the dominant methanogens in reactors inoculated with L-AD effluent, WAS, and AGS, respectively. These findings suggest among the three inoculum, L-AD effluent is the most effective inoculum for SS-AD of on farm organic waste.

Effect of inoculated and uninoculated aeration pretreatment on nutrients and phytotoxicity of anaerobic digestion effluent

This study investigates the influence of inoculated and uninoculated aeration pretreatment on nutrients and phytotoxicity of anaerobic digestion (AD) effluent. Swine manure AD effluent was inoculated with activated and anaerobic sludge, respectively. Our results show that aeration with the addition of activated sludge could reduce the phytotoxicity of AD effluent. Compared to the control treatment without any sludge addition, the addition of activated sludge resulted in a more significant reduction in the AD effluent salinity, NH4+ content, and organic matter (indicated by the chemical oxygen demand) when AD effluent was aerated for less than 8 hours. As a result, a much higher seed germination index (GI) was observed for the treatment with activated sludge addition, particularly when aerated for 4–5 hours, contributing the gas/water ratio of 20:1–30:1. On the other hand, no significant differences in the nutrient contents and GI value were observed for the control treatment and that with the addition of anaerobic sludge. Results from this study shed light on optimizing the management of AD effluent for agricultural application.

Effects of phosphogypsum, superphosphate, and dicyandiamide on gaseous emission and compost quality during sewage sludge composting

This study investigated the effects of phosphogypsum, superphosphate, and dicyandiamide on gaseous emission and compost quality during sewage sludge composting. Results showed that phosphogypsum reduced ammonia (NH3) and methane (CH4) emissions but increased nitrous oxide (N2O) emission. Superphosphate simultaneously reduced NH3, N2O and CH4 emissions. Dicyandiamide markedly reduced N2O emission during composting. Combination of phosphogypsum and dicyandiamide reduced CH4 and N2O emissions by 75.6% and 86.4%, while NH3 emission was increased by 22.0%. Combination of superphosphate and dicyandiamide reduced NH3, CH4 and N2O emissions by 12.3%, 81.0% and 88.2%, respectively. More importantly, with the addition of 10% initial raw materials, phosphogypsum and superphosphate conserved nitrogen and improved compost quality by introducing additional nutrients.