Guoxue Li

Effect of aeration rate, C/N ratio and moisture content on the stability and maturity of compost

To estimate the order of importance of factors affecting the stability and maturation of compost, pig feces and corn stalks were co-composted at different aeration rates (AR: 0.24, 0.48, 0.72 L kg(-1)dry matter (DM)min(-1)), C/N ratios (15, 18, 21), and moisture contents (MC: 65%, 70%, 75%). The thermophilic phase with all treatments was long enough to meet sanitation requirements. The oxygen content and N losses increased with increasing AR, but no significant differences were observed between the moderate and high treatments. The compost with the lowest initial C/N ratio was significantly different from the other treatments and had the lowest germination index (53-66%). AR was the main factor influencing compost stability, while the C/N ratio mainly contributed to compost maturity, and the MC had an insignificant effect on the compost quality. The recommended parameters for composting are an AR of 0.48 L kg(-1) DM min(-1) and a C/N ratio of 18 with MCs of 65-75%.

Effect of C/N ratio, aeration rate and moisture content on ammonia and greenhouse gas emission during the composting

Gaseous emission (N2O, CH4 and NH3) from composting can be an important source of anthropogenic greenhouse gas and air pollution. A laboratory scale orthogonal experiment was conducted to estimate the effects of C/N ratio, aeration rate and initial moisture content on gaseous emission during the composting of pig faeces from Chinese Ganqinfen system. The results showed that about 23.9% to 45.6% of total organic carbon (TOC) was lost in the form of CO2 and 0.8% to 7.5% of TOC emitted as CH4. Most of the nitrogen was lost in the form of NH3, which account for 9.6% to 32.4% of initial nitrogen. N2O was also an important way of nitrogen losses and 1.5% to 7.3% of initial total nitrogen was lost as it. Statistic analysis showed that the aeration rate is the most important factor which could affect the NH3 (p = 0.0189), CH4 (p = 0.0113) and N2O (p = 0.0493) emissions significantly. Higher aeration rates reduce the CH4 emission but increase the NH3 and N2O losses. C/N ratio could affect the NH3 (p = 0.0442) and CH4 (p = 0.0246) emissions significantly, but not the N2O. Lower C/N ratio caused higher NH3 and CH4 emissions. The initial moisture content can not influence the gaseous emission significantly. Most treatments were matured after 37 days, except a trial with high moisture content and a low C/N ratio.

Influence of aeration on CH4, N2O and NH3 emissions during aerobic composting of a chicken manure and high C/N waste mixture

Co-composting of chicken manure, straw and dry grasses was investigated in a forced aeration system to estimate the effect of aeration rates on NH(3), CH(4) and N(2)O emissions and compost quality. Continuous measurements of gas emissions were carried out and detailed gas emission patterns were obtained using an intermittent-aeration of 30 min on/30 min off at rates of 0.01 (A1), 0.1 (A2) and 0.2 (A3) m(3)min(-1)m(-3). Concentrations of CH(4) and N(2)O at the low aeration rate (A1) were significantly greater than those at the other two rates, but there was no significant difference between the A2 and A3 treatments. CH(4) and N(2)O emissions for this mixture could be controlled when the composting process was aerobic and ammonia emissions were reduced at a lower aeration rate. Comparison of CH(4), N(2)O, NH(3) emissions and compost quality showed that the aeration rate of the A2 treatment was superior to the other two aeration rates.

Feasibility of Using Coal Ash Residues as CO-Composting Materials for Sewage Sludge

Alkaline coal ash residues produced from a coal-fired power plant were co-composted with sewage sludge to evaluate its effect on heavy metal availability and the biological process of composting. Coal fly ash (FA) and lagoon ash (LA) were mixed with dewatered sludge at 0, 10 and 25% w/w, and the mixtures were composted for 100 days in laboratory batch reactors. The changes in pH, electrical conductivity (EC), CO2 production, microbial population, soluble and extractable heavy metal contents were measured during the composting period. Following an initial increase, pH started to decrease from day 7 onward till the end of the composting period for all treatments. Sludge with coal fly ash amendment had a higher pH and EC than those of the control and LA-sludge composts. Increasing fly ash amendment levels resulted in a significant reduction in DTPA-extractable Cd, Cu, Zn, Mn and Pb contents of the FA-sludge composts while the reduction was less obvious in the LA-sludge composts. No significant difference in...

Changes in biological parameters during co-composting of sewage sludge and coal ash residues

Coal ash residues, including fly ash (FA) and lagoon ash (LA), were co-composted with dewatered sludge for 100 days in a bench-scale composting system and biological parameters were monitored to evaluate the effect of ash residues on the composting process. Coal ash residue amendment caused a rise in alkalinity and salinity, but had no adverse effect on the population of thermophilic bacteria except for 25% FA amendment. All enzyme activities decreased with composting time. β-glucosidase and alkaline phosphatase activities were reduced with an increase in ash residue amendment, while no significant reduction was noted for urease and dehydrogenase activities after 20 days of incubation. Positive correlations were obtained among β-glucosidase, alkaline phosphatase and urease activities, while no correlation was found between thermophilic bacteria and enzyme activities. With the exception of 25% FA-amended sludge compost, addition of coal ash residues in sewage sludge is feasible and showed little effects on metabolic activity during composting process.

Effects of phosphogypsum and superphosphate on compost maturity and gaseous emissions during kitchen waste composting.

This study investigated the effects of phosphogypsum and superphosphate on the maturity and gaseous emissions of composting kitchen waste. Two amended compost treatments were conducted using phosphogypsum and superphosphate as additives with the addition of 10% of initial raw materials (dry weight). A control treatment was also studied. The treatments were conducted under aerobic conditions in 60-L reactors for 35 days. Maturity indexes were determined, and continuous measurements of CH4, N2O, and NH3 were taken. Phosphogypsum and superphosphate had no negative effects on compost maturity, although superphosphate inhibited the temperature rise in the first few days. The addition of phosphogypsum and superphosphate drastically reduced CH4 emissions (by 85.8% and 80.5%, respectively) and decreased NH3 emissions (by 23.5% and 18.9%, respectively). However, a slight increase in N2O emissions (by 3.2% and 14.8%, respectively) was observed. Composting with phosphogypsum and superphosphate reduced total greenhouse gas emissions by 17.4% and 7.3% respectively.

Emission of volatile sulfur compounds during composting of municipal solid waste (MSW)

Volatile sulfur compounds (VSCs) are the main source for malodor from composting plants. In this study, the VSCs generated from composting of 15-80 mm municipal solid waste (T0), kitchen waste (T1) and kitchen waste mixed dry cornstalks (T2) were measured in 60 L reactors with forced aeration for a period of 30 days. The VSCs detected in all treatments were hydrogen sulfide (H2S), methyl mercaptan (MM), dimethyl sulfide (DMS), carbon bisulfide (CS2) and dimethyl disulfide (DMDS). Over 90% of the VSCs emissions occurred during the first 15 days, and reached their peak values at days 4-7. The emission profiles of five VSCs species were significantly correlated with internal materials temperature and outlet O2 concentration (p<0.05). Total emissions of the VSCs were 216.1, 379.3 and 126.0 mg kg(-1) (dry matter) for T0, T1 and T2, respectively. Among the five VSCs, H2S was the most abundant compound with 39.0-43.0% of total VSCs released. Composting of kitchen waste from separate collection posed a negative influence on the VSC and leachate production because of its high moisture content. An addition of dry cornstalks at a mixing ratio of 4:1 (wet weight) could significantly reduce the VSCs emissions and avoid leachate. Compared to pure kitchen waste, VSCs were reduced 66.8%.

Impact of struvite crystallization on nitrogen losses during composting of pig manure and cornstalk.

An absorbent mixture of magnesium hydroxide (Mg(OH)(2)) and phosphoric acid (H(3)PO(4)) was added to compost mixtures of pig manure with cornstalk in different molar ratios (T1, 1:1; T2, 1:2; T3, 1:3) in order to examine its effect on controlling ammonia losses during composting. Based on the principle of struvite precipitation, and with an unamended trial as control (CK), an in-vessel composting experiment was conducted in fermenters (60L with forced aeration) in which the absorbent mixture was added with proportions of 3.8%, 7.3% and 8.9% of dry weight for T1, T2 and T3, respectively. The results showed that the total nitrogen loss was reduced from 35% to 12%, 5% and 1% of initial N mass, respectively. In the final compost, the total nitrogen content in T1, T2 and T3 was improved by 10, 14, 12gkg(-1), and NH(4)(+)-N in T1, T2 and T3 was improved by 8, 9, and 10gkg(-1), respectively, compared with the unamended trial. The results of the germination index test showed that the maturity of treatment T2 was best among the four treatments in the final compost, followed by T1, CK and T3. The results of X-ray diffraction (XRD) confirmed the formation of magnesium ammonium phosphate hexahydrate (MgNH(4)PO(4).6H(2)O:MAP) in the T1, T2 and T3 compost. Based on these results, the adsorbent mixture of Mg(OH)(2)+H(3)PO(4) could control nitrogen loss effectively during composting via struvite crystallization. However, an excess of phosphoric acid (1:3) had a negative influence on composting properties. The pH value decreased which led to reduced microorganism activity, and which finally resulted in reduced biodegradation of the organic matter.

Chemical Evaluation of Sewage Sludge Composting as a Mature Indicator for Composting Process

Several chemical parameters were studied during a 100 daysperiod in order to identify parameters that can be used asindicators of compost maturity. One treatment was a mixture ofsewage sludge and sawdust (TS); another was a mixture of sewagesludge, pig manure and sawdust (TS-PM). The pH of water extractsincreased during the thermophilic phase and then decreased in twotreatments. While the electrical conductivity (EC) decreasedthroughout the composting time. The 4.99% in the change ofvolatile matter of TS-PM was higher than 1.73% in that of TS,at the same time, the change of organic carbon were 5.04% inTS-PM more than 3.82% of TS. Total nitrogen content in TS andTS-PM had a markedly increase tendence during composting, andthe change in TS-PM was very more obvious than in TS, soreduction of C/N ratio in TS-PM was higher than in TS, C/Nratio of TS-PM and TS was 14.39 and 18.57 in mature production,respectively. Carbon content in HA plus FA and HA in twocomposts decreased from 0 to 100 day, but carbon content of FAdecreased, so HA-C/FA-C ratio, HR, HI has a markedly increase inTS and TS-PM, and the parameters in TS-PM were higher than inTS. The points expressing maturity degree in TS-PM was more inTS. The nitrogen content of HA plus and HA showed a increasedtendence in TS and TS-PM, the change of nitrogen of thesefractions in TS-PM was higher than in TS, so C/N ratio of allfractions including HA plus FA, HA and FA, indicated a reductiontendence, and the refuction in FA was larger than in HA. E4/E6ratio of HA plus FA and HA decreased during composting, and one FA was increase. E4/E6 ratio of HA plus FA and HA in TS-PM wasvery smaller than in TS, HA in TS-PM was a larger molecular sizethan HA in TS. The changes of organic matter compositions incomposting: the crude fat and carbohydrates had a markedlyreduction and cellulose plus hemicellulose had a slight decrease;crude protein and lignin content in TS and TS-PM had an increasetendence.

Effects of aeration rate on maturity and gaseous emissions during sewage sludge composting.

This study investigated effects of aeration rate (AR) on maturity and gaseous emissions during sewage sludge composting, sewage sludge and corn stalks as the bulking agent were co-composted at different ARs (0.1, 0.2, 0.3L·kg(-1) dry matter (DM)·min(-1)). The thermophilic phase for the low and moderate AR treatments was able meet sanitation requirements, but too short to meet sanitation requirements in the high AR treatment. The high AR treatment was significantly different from the other treatments, and had the lowest electrical conductivity and highest E4/E6(absorbance ratio of wavelength 465 and 665nm). The AR influences the nitrogen variations; high AR compost had the highest NH4(+)-N content and lowest NOx(-)-N content. The AR was the main factor influencing compost stability, but the AR had little impact on pH and the germination index. The moderate AR treatment had the highest NH3 emissions during composting, while the low AR treatment had the highest CH4 and N2O emissions. Based on our comprehensive investigation, the recommended AR for sludge composting is 0.2L·kg(-1) DM·min(-1).