Pyrolysis-A tool in the wastewater solids handling portfolio, not a silver bullet: Benefits, drawbacks, and future directions.

Pyrolysis is the process whereby carbonaceous materials, such as biosolids, are heated between 400°C and 900°C in the absence of oxygen. Three main products are generated: a solid product called biochar, a py-liquid that consists of aqueous phase and non-aqueous phase liquid, and py-gas. The biochar holds value as a beneficial soil amendment and sequesters carbon. The py-liquid is potentially hazardous and needs to be dealt with (including potentially reducing it on-site via catalysis or thermal oxidation). Py-gas can be used on-site for energy recovery. Pyrolysis has gained recent interest due to concern over per- and polyfluoroalkyl substances (PFAS) in biosolids. Although pyrolysis can remove PFAS from biosolids, it has been shown to produce PFAS that reside in py-liquid, and the fate in py-gas remains a knowledge gap. More research is needed to help close the PFAS and fluorine mass balance through pyrolysis influent and effluent products because pyrolysis alone does not destroy all PFAS. The moisture content of biosolids substantially affects the energy balance for pyrolysis. Utilities that already produce a dried biosolids product are in a better position to install pyrolysis. Pyrolysis has both defined benefits (solids reduction, PFAS removal from biosolids, and biochar production) as well as remaining questions (the fate of PFAS in py-gas and py-liquid, mass balance on nutrients, and py-liquid handling options) that will be answered through more pilot and full-scale demonstrations. Regulations and local policies (such as carbon sequestration credits) could affect pyrolysis implementation. Pyrolysis should be considered as an option in the biosolids stabilization toolbox with application being based on individual circumstances of a utility (e.g., energy, moisture content of biosolids, PFAS). PRACTITIONER POINTS: Pyrolysis has known benefits but limited full-scale operational data. Pyrolysis removes PFAS from biochar, but PFAS fate in gas phase is unknown. Moisture content of influent feed solids affects energy balance of pyrolysis. Policy on PFAS, carbon sequestration, or renewable energy could impact pyrolysis.

Crystal-Plane Controlled Spontaneous Polarization of Inorganic Perovskite toward Boosting Triboelectric Surface Charge Density.

Triboelectric generators (TENGs) have been extensively studied as a new energy for low cost and the universally applicable prospect. Meanwhile, perovskites have been applied in TENG and show a good performance in view of high carrier mobility, long life and dielectric properties. The asymmetry structure of the orthogonal phase CsPbBr3 perovskite endows it with ferroelectric property and induces the misalignment of the positive and negative charge centers. Herein, the surface energy of halogen doped inorganic CsPbX3 (X = Cl-, Br-) perovskites are theoretically investigated by density functional theory (DFT) calculation, the crystal polarizability of pristine CsPbBr3 is improved from 0.47 Ry a.u. to 0.52 Ry a.u. (CsPbCl3), indicating the polarizability of CsPbCl3 is higher than CsPbBr3. In addition, the build-in electric field (Ebuild-in) of perovskite materials can be enhanced by the spontaneous polarization and the aligned dipoles in the Ebuild-in could further improve the tribo-electrostatic electric field by retaining more triboelectric surface charges. In the end, CsPbCl3 achieved a power of 3.06 W m-2 compared to the power of 1.34 W m-2 of CsPbBr3. This work focuses on the regulation of crystal planes using spontaneous polarization of perovskite toward achieving a high built-in electric field for enhancing triboelectric surface charge density.

Rapid evaluation of leaching potential of heavy metals from municipal solid waste incineration fly ash.

Municipal solid waste incineration fly ash is directly landfilled after solidification in the industry. The rapid evaluation of contaminant leaching is required before the landfill of fly ash. In order to reduce the time to evaluate the effect of solidification, a set of rapid evaluation method was developed through the determination of characteristic index, heavy metal leaching analysis, principal component analysis, and mathematical model construction. It was found that f-CaO, acid neutralizing capacity, pH and soluble calcium were negatively correlated with heavy metal leaching. The soluble chlorine was positively correlated with heavy metal leaching. The effect of each feature indicators on heavy metal leaching was evaluated using principal component analysis and mathematical analysis software R.3.4.4. Furthermore, R.3.4.4 was used to detect the optimal model and the excess probability formula by stepwise linear regression and logistic regression analysis method. By introducing the measured value of feature indicator into the excess probability formula, the rate of excess-standard of heavy metals leaching can be preliminarily determined. Based on the above ideas, a rapid detection and evaluation system could be developed according to the local leaching standards and the components of fly ash selected locally.

Autocatalytic Pyrolysis of Wastewater Biosolids for Product Upgrading.

The main goals for sustainable water resource recovery include maximizing energy generation, minimizing adverse environmental impacts, and recovering beneficial resources. Wastewater biosolids pyrolysis is a promising technology that could help facilities reach these goals because it produces biochar that is a valuable soil amendment as well as bio-oil and pyrolysis gas (py-gas) that can be used for energy. The raw bio-oil, however, is corrosive; therefore, employing it as fuel is challenging using standard equipment. A novel pyrolysis process using wastewater biosolids-derived biochar (WB-biochar) as a catalyst was investigated to decrease bio-oil and increase py-gas yield for easier energy recovery. WB-biochar catalyst increased the py-gas yield nearly 2-fold, while decreasing bio-oil production. The catalyzed bio-oil also contained fewer constituents based on GC-MS and GC-FID analyses. The energy shifted from bio-oil to py-gas, indicating the potential for easier on-site energy recovery using the relatively clean py-gas. The metals contained in wastewater biosolids played an important role in upgrading pyrolysis products. The Ca and Fe in WB-biochar reduced bio-oil yield and increased py-gas yield. The py-gas energy increase may be especially useful at water resource recovery facilities that already combust anaerobic digester biogas for energy since it may be possible to blend biogas and py-gas for combined use.

Pyrolysis of Dried Wastewater Biosolids Can Be Energy Positive.

Pyrolysis is a thermal process that converts biosolids into biochar (a soil amendment), py-oil and py-gas, which can be energy sources. The objectives of this research were to determine the product yield of dried biosolids during pyrolysis and the energy requirements of pyrolysis. Bench-scale experiments revealed that temperature increases up to 500 °C substantially decreased the fraction of biochar and increased the fraction of py-oil. Py-gas yield increased above 500 °C. The energy required for pyrolysis was approximately 5-fold less than the energy required to dry biosolids (depending on biosolids moisture content), indicating that, if a utility already uses energy to dry biosolids, then pyrolysis does not require a substantial amount of energy. However, if a utility produces wet biosolids, then implementing pyrolysis may be costly because of the energy required to dry the biosolids. The energy content of py-gas and py-oil was always greater than the energy required for pyrolysis.

A simple kinetic analysis of syngas during steam hydrogasification of biomass using a novel inverted batch reactor with instant high pressure feeding.

A newly designed inverted batch reactor equipped with a pressure-driven feeding system was built for investigating the kinetics of syngas during the steam hydrogasification (SHR) of biomass. The system could instantly load the feedstock into the reactor at high temperature and pressure, which simulated the way to transport the feedstock into a hot and pressurized gasifier. Experiments were conducted from 600°C to 700°C. The inverted reactor showed very high heating rate by enhancing the carbon conversion and syngas production. The kinetic study showed that the rates of CH4, CO and CO2 formation during SHR were increased when the gasification temperature went up. SHR had comparatively lower activation energy for CH4 production. The activation energies of CH4, CO and CO2 during SHR were 42.8, 51.8 and 14kJ/mol, respectively.

[Distribution character of synthetic musks in urban sewage sludges].

The characteristics of occurrence and distribution of 8 synthetic musks in 15 sewage sludges in Shanghai were studied. The results indicated that HHCB and AHTN were the two main components in all sludges, with the mean concentration of 2.92 mg x kg(-1) (0.81-6.39 mg x kg(-1)) and 1.96 mg x kg(-1) (0.35-3.11 mg x kg(-1)), respectively; and the concentrations of ADBI, AHMI, MK were less. The distributions detected in sludges are in accordance with the usage patterns in China. Total concentrations of 8 synthetic musks were ranged from 1.16-9.57 mg x kg(-1), which were lower than the results in previous studies. Concentrations in sludges are influenced by ratio of domestic wastewater in influent, sewage load and sewage treatment methods. The good linear relationships among HHCB, AHTN and ADBI indicate that these components have the same source: domestic wastewater. The consumption rates of HHCB and AHTN connected to per inhabitant in Shanghai region were estimated, which are low compared with those found in European. The potential impacts on agricultural soil were also assessed.

Characteristic of a novel composite inorganic polymer coagulant-PFAC prepared by hydrochloric pickle liquor.

A composite inorganic polymer coagulant, polyferric aluminum chloride (PFAC) was prepared by using hydrochloric pickle liquor and calcium aluminate as main materials. The optimum conditions for preparing PFAC with the hydrochloric pickle liquor and the calcium aluminate were studied. The coagulation performance of PFAC was investigated by studying the turbidity, COD, total phosphate (TP) and NH(3)-N removal efficiency in municipal sewage treatment. Results indicated that the effective composition, basicity (simplified as B, B=[OH]/(3[Fe(T)+Al(T)])x100%), coagulation performance and stability of PFAC were affected by calcium aluminate dosage, reaction time, reaction temperature and stabilizing agents. The COD and turbidity removal efficiency of PFAC was better than that of PFS and FeCl(3), and the TP and NH(3)-N removal efficiency of PFAC was much better than that of PFS, FeCl(3) and PAC. PFAC not only possessed a good coagulation performance, but also had good stability when stored.

Improvement of ground granulated blast furnace slag on stabilization/solidification of simulated mercury-doped wastes in chemically bonded phosphate ceramics.

This paper investigated the effectiveness of (ground granulated blast furnace slag) GGBFS-added chemically bonded phosphate ceramic (CBPC) matrix on the stabilization/solidification (S/S) of mercury chloride and simulated mercury-bearing light bulbs (SMLB). The results showed that the maximal compressive strength was achieved when 15% and 10% ground GGBFS was added for HgCl(2)-doped and SMLB-doped CBPC matrices, respectively. The S/S performances of GGBFS-added matrices were significantly better than non-additive matrices. As pore size was reduced, the leaching concentration of Hg(2+) from GGBFS-added CBPC matrix could be reduced from 697 microg/L to about 3 microg/L when treating HgCl(2). Meanwhile, the main hydrating product of GGBFS-added matrices was still MgKPO(4).6H(2)O. The improvement of S/S effectiveness was mainly due to physical filling of fine GGBFS particles and microencapsulation of chemical cementing gel.