Screening of early warning indicators for full-scale dry anaerobic digestion of household kitchen waste.

Process monitoring is an essential measure to achieve efficient and stable performance in anaerobic digestion, thus requiring identification of effective early warning indicators. However, the application of early warning indicators to full-scale dry anaerobic engineering biogas plant still remains elusive. This study evaluated the effectiveness of common early warning indicators (including CH4, CO2, H2S, volatile fatty acids (VFAs), alkalinity (ALK), total ammonia concentration (TAN) and free ammonia concentration (FAN)) in monitoring the instability of anaerobic digestion process at a practical engineering plant. The results showed that the individual indicators could not provide a sufficient early warning time before the digester fell into failure collapse. In comparison, the coupling indicators (the ratio of CH4/CO2, CH4/pH, and CH4/H2S) had sensitive response to perturbation, which could regard as a potential early warning indicator, with the early warning time of 6, 7 and 10 days, respectively. Moreover, the VFA/ALK could be used as auxiliary indicators due to the limitation of complex detection methods. In addition, the result also indicated that the application of some warning indicators needs to be further verified, when transferring the result of laboratory scale to the practice application scenarios. This study provides insight into the stable operation of dry anaerobic engineering.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting.

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS2 and ZnCu(P2O7) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ±â€¯11.8%, which was the highest among all treatments.

Emission of odor pollutants and variation in microbial community during the initial decomposition stage of municipal biowaste.

Odor pollution often occurs in the initial decomposition stage of municipal biowaste, including throwing/collection and transportation. However, this aspect of odor impact from municipal biowaste has not been well studied. In this study, a practical dustbin (120 L) equipped with flux chamber and filled with three types of municipal biowaste was used to simulate garbage storage conditions. The result indicated that the emission rate of odor pollutants for uncooked food waste (UFW) represented a nearly linear growth trend, reaching the maximum (3963 ± 149 µg kg-1 DM h-1) at 72 h. Cooked food waste (CFW) increased rapidly from 8 h to 24 h, and then remain fluctuated, reached the maximum (2026 ± 77 µg kg-1 DM h-1) at 72 h. Comparatively, household kitchen waste (HKW) reached the maximum emission rate (10,396 ± 363 µg kg-1 DM h-1) at 16 h. Sulfide and aldehydes ketones were identified as dominant odor contributor to UFW and CFW, respectively. While aldehydes ketones and sulfides were both dominant odor contributor to HKW. Moreover, the microbial diversity analysis suggests that Acinetobacter was the dominant genus in UFW, and Lactobacillus was the dominant genus in CFW and HKW. In addition, it was evident that each odorous pollutant was significantly associated with two or more bacterial genera, and most bacterial genera such as Acinetobacter, were also significantly associated with multiple odorous pollutants. The variation of odorants composition kept consistent with microbial composition. The present study could provide essential evidence for a comprehensive understanding of odorant generation in the initial decomposition stage of municipal biowaste. It could contribute to setting out strategies for odor control and abatement in municipal biowaste management systems.

Microbial volatile organic compounds as novel indicators of anaerobic digestion instability: Potential and challenges.

The wide application of anaerobic digestion (AD) technology is limited by process fluctuations. Thus, process monitoring based on screening state parameters as early warning indicators (EWI) is a top priority for AD facilities. However, predicting anaerobic digester stability based on such indicators is difficult, and their threshold values are uncertain, case-specific, and sometimes produce conflicting results. Thus, new EWI should be proposed to integrate microbial and metabolic information. These microbial volatile organic compounds (mVOCs) including alkanes, alkenes, alkynes, aromatic compounds are produced by microorganisms (bacteria, archaea and fungi), which might serve as a promising diagnostic tool for environmental monitoring. Moreover, mVOCs diffuse in both gas and liquid phases and are considered the language of intra kingdom microbial interactions. Herein, we highlight the potential of mVOCs as EWI for AD process instability, including discussions regarding characteristics and sources of mVOCs as well as sampling and determination methods. Furthermore, existing challenges must be addressed, before mVOCs profiling can be used as an early warning system for diagnosing AD process instability, such as mVOCs sampling, analysis and identification. Finally, we discuss the potential biotechnology applications of mVOCs and approaches to overcome the challenges regarding their application.

Effects of lactic acid on modulating the ammonia emissions in co-composts of poultry litter with slaughter sludge.

The aim of this work was to study the feasibility of lactic acid addition during poultry litter and slaughter sludge composting for controlling NH3 emissions. The results indicated that lactic acid addition reduced NH3 emissions and promoted the maturity of the composting product. Compared to the blank, nitrogen loss in the form of NH3 emissions in the 0.4%, 0.7%, and 1.0% lactic acid treatments decreased by 3.36%, 8.29%, and 14.65%, respectively. Moreover, lactic acid addition promoted the relative abundance of Lactobacillales, while the microbial community of the blank was dominated by Bacillales. The mechanism behind the control of NH3 emissions via the addition of lactic acid involved the secretion of large amounts of lactic acid by Lactobacillales, which lowers the pH of the initial compost pile. This study suggests that lactic acid is a suitable additive for composting.

Emission characteristics of VOCs and potential ozone formation from a full-scale sewage sludge composting plant.

Volatile organic compounds (VOCs) are the major components of the odor emitted from sewage sludge composting plants and are generally associated with odorous nuisances and health risks. However, few studies have considered the potential ozone generation caused by VOCs emitted from sewage sludge composting plants. This study investigated the VOC emissions from a full-scale composting plant. Five major treatment units of the composting plant were chosen as the monitoring locations, including the dewatered room, dewatered sludge, blender room, fermentation workshop, and product units. The fermentation workshop units displayed the highest concentration of VOC emissions at 2595.7 ±â€¯1367.3 µg.m-3, followed by the blender room, product, dewatered sludge, and dewatered room units, whose emissions ranged from 142.2 ±â€¯86.8 µg.m-3 to 2107.6 ±â€¯1045.6 µg.m-3. The detected VOC families included oxygenated compounds, alkanes, alkenes, sulfide compounds, halogenated compounds, and aromatic compounds. Oxygenated compounds, particularly acetone, were the most abundant compounds in all samples. Principal component analysis revealed that the dewatered room and dewatered sludge units clustered closely, as indicated by their similar component emissions. The product units differed from the other sampling units, as their typical compounds were methanethiol, styrene, carbon disulfide, and hexane, all of which were the products of the latter stages of composting. Among the treatment units, the fermentation workshop units had the highest propylene equivalent (propy-equiv) concentration. Dimethyl disulfide and limonene were the major contributors. Limonene had the highest propy-equiv concentration, which contributed to the increased atmospheric reactivity and ozone formation potential in the surrounding air. To control the secondary environmental pollution caused by the VOC emissions during sewage sludge composting, the emission of limonene and dimethyl disulfide must be controlled from the blender room and fermentation workshop units.

Application of ceramsite and activated alumina balls as recyclable bulking agents for sludge composting.

Composting is a major sludge-treatment method and bulking agents are very important in sludge composting. In this study, ceramsite and activated alumina balls were chosen as recyclable bulking agents for sludge composting. Variations in the temperature, pH, electrical conductivity, organic matter, dissolved organic carbon, moisture content, and heavy metals were detected during composting with different bulking-agent treatments as well as differences in the germination index values. The results showed that both bulking agents could ensure the maturity of the compost; further, ceramsite treatment resulted in the best water removal efficiency. According to the sequential extraction procedure, both ceramsite and activated alumina balls could stabilize Cd but they also increased the mobility of Zn. After comparing the effects of different particle sizes of ceramsite on composting, 20 mm was determined to be the most optimal value. Additionally, the recovery rates of ceramsite and activated alumina balls were 96.9% and 99.9%, respectively.

Emission characteristics and health risk assessment of volatile organic compounds produced during municipal solid waste composting.

Municipal solid waste degradation during composting generates volatile organic compounds (VOCs), which can pose health risks the staff at the composting site and people living nearby. This problem restricts the widespread application of composting techniques. The characteristics of VOCs emitted from different units at a composting plant and the health risks posed were investigated in this study. A total of 44 VOCs (including alkanes, alkenes, aromatic compounds, halogenated compounds, oxygenated compounds, and sulfur-containing compounds) were identified and quantified. The highest VOC concentration (15484.1 ±â€¯785.3 µg/m3) was found in primary fermentation, followed by the tipping unit (10302.1 ±â€¯1334.8 µg/m3), composting product (4693.6 ±â€¯1024.3 µg/m3), secondary fermentation (929.9 ±â€¯105.2 µg/m3), and plant boundary (370.4 ±â€¯75.8 µg/m3). The mean VOC concentration was 6356.0 µg/m3. The main compounds emitted during primary fermentation were oxygenated and those emitted from the tipping unit were alkenes. Health risk assessments indicate that VOCs did not pose unacceptable non-carcinogenic risks i.e., the HR values were <1 and carcinogenic risks (CR) values were <1.0 × 10-4. These results indicate that VOC emissions do not pose health risks to the staff at the composting site or to people living nearby. However, the cumulative non-carcinogenic and carcinogenic risks posed by the VOC mixture were high, especially for the primary fermentation unit emissions. Therefore, protecting the staff working near the primary fermentation unit should be a priority. Measures should be taken to minimize cumulative non-carcinogenic and carcinogenic risks because people are exposed to a mixture of VOCs mixture rather than to a single type of VOC.

[Emission Characteristics and Ozone Formation Potential of VOCs from a Municipal Solid Waste Composting Plant].

In Beijing, the chemical composition and component concentrations of volatile organic compounds (VOCs) were investigated during the municipal solid waste composting process using a portable gas chromatograph coupled with a mass spectrometer. The contributions of VOCs to the ozone formation potential were computed using the maximum incremental reactivity (MIR) scale and the propylene-equivalent concentration scale. The results showed that the concentrations of waste discharge in the sorting room, the first fermentation workshop, the second fermentation workshop, the compost product workshop, and the plant boundary were 10302.1, 15484.1, 929.9, 4693.6 and 370.4 µg·m-3, respectively. The main VOCs of the municipal solid waste composting plant were ethanol, limonene, and acetone. The propylene-equivalent concentrations of waste discharge in the sorting room, the first fermentation workshop, the second fermentation workshop, the compost product workshop, and the plant boundary were 25875.7, 4087.9, 378.0, 747.7 and 296.8 µg·m-3, whereas the O3 formation potentials computed using the MIR scale were 26979.3, 21168.3, 1469.3, 6439.6 and 455.8 µg·m-3. Reducing pollution by controlling the VOCs emission of waste discharge in the sorting room and the first fermentation workshop is important and can decrease the ozone formation potential. Given the accuracy and accessibility of the method, the MIR scale is more suitable for calculating the ozone formation potential of VOCs emitted from the municipal solid waste composting plant.