Guoren Xu

Recycle of Alum recovered from water treatment sludge in chemically enhanced primary treatment

An investigation was made to study the feasibility of recovering the Alum from coagulation sludges and reusing it in chemically enhanced primary treatment (CEPT) process to make the CEPT more cost-effective and recover the resource (Alum) efficiently. The optimum condition and efficiency of the acidification method for Alum recovery from coagulation sludge were investigated in the test. The results show that when the recovery rate of Alum reaches its highest level, 84.5%, the reduction rate of sludge is 35.5%. It turns out that the capability of recovered coagulant to remove turbidity, UV(254) and COD are 96%, 46% and 53%, respectively. The results prove that the recovered coagulants could be used in CEPT and the efficiency of recovered coagulant to remove pollutants is similar to that of fresh coagulant. Although some substances will be enriched during recycle, they have little effect on the quality of treated wastewater. The experiments verify that it would be an advisable and cost-effective way to recover Alum from coagulation sludges in water treatment and chemical wastewater treatment, and it could be then recycled to CEPT as well as reduce sludge volume.

Development of sludge-based adsorbents: Preparation, characterization, utilization and its feasibility assessment

The increasing generation of sludge and its subsequent treatment are very sensitive environmental problems. For a more stable and sustainable treatment of sludge, there have been many studies, including the conversion of sludge into sludge-based adsorbents (SBAs) for pollutants removal. In this review, current SBAs preparation conditions and use as adsorbent for contaminant removal in water treatment are summarized and discussed. Carbonization, physical activation and chemical activation are three common preparation methods. The controlling key parameters include pyrolysis temperature, dwell time, heating rate, activator and feedstock type. The efficacy of SBAs in contaminant adsorption depends on their surface area, pore size distribution, surface functional groups and ion-exchange capacity. It has been demonstrated that SBAs can attain high uptakes of dyes and metal ions due to their high cation exchange capacity; whereas the strong antibiotics adsorption performance of SBAs derives from high degree of mesoporosity. In addition, thermal treatment significantly stabilizes heavy metals contained in sludge. The paper also discusses the economic feasibility and environmental safety of preparation and application of SBAs. Further research will include investigations on the migration and transformation of element in sludge by thermal treatment, more economical and efficient chemical activation reagents, obtaining SBAs for designated application, combination of coagulation and SBAs adsorption, regeneration of SBAs and full-scale tests.

Stabilization of heavy metals in lightweight aggregate made from sewage sludge and river sediment.

The primary goal of this research is to investigate the stabilization of heavy metals in lightweight aggregate (LWA) made from sewage sludge and river sediment. The effects of the sintering temperature, the (Fe₂O₃+CaO+MgO)/(SiO₂+Al₂O₃) ratio (K ratio), SiO₂/Al₂O₃ and Fe₂O₃/CaO/MgO (at fixed K ratio), pH, and oxidative conditions on the stabilization of heavy metals were studied. Sintering at temperatures above 1100 °C effectively binds Cd, Cr, Cu and Pb in the LWA, because the stable forms of the heavy metals are strongly bound to the aluminosilicate or silicate frameworks. Minimum leachabilities of Cd, Cr, Cu and Pb were obtained at K ratios between 0.175 and 0.2. When the LWA was subjected to rigorous leaching conditions, the heavy metals remained in the solid even when the LWA bulk structure was broken. LWA made with sewage sludge and river sediment can therefore be used as an environmentally safe material for civil engineering and other construction applications.

Surface properties and adsorption characteristics to methylene blue and iodine of adsorbents from sludge.

Adsorbent materials created from wastewater sludge have unique surface characteristics and could be effective in adsorption applications. In this research, the sludge-adsorbents were generated by pyrolyzing mixtures of sewage sludge and H(2)SO(4). Scanning electron microscope (SEM), thermal analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) were used to analyze the properties of sludge-adsorbent. XPS results show that the adsorbent surface functional groups with high contents of oxygen-containing groups serve as active sites for the adsorption and affect the surface characteristics; the adsorption mechanism of methylene blue (MB) is mainly Brönsted acid-base reaction between the adsorbent surface and MB; and iodine atoms are bonded to the surface of the adsorbent mainly by dispersive interactions rather than by electrostatic interactions. The results also show that H(2)SO(4) level, pyrolysis temperature and sulfuric acid/sludge weight ratio actually affected the adsorption characteristics. Using the conditions (H(2)SO(4) level of 1-18 M, pyrolysis temperature of 650°C, and weight ratio of 0.8), the adsorption capacities for MB and iodine were 74.7-62.3 mg g(-1) and 169.5-209.3 mg g(-1), respectively.

Ferric coagulant recovered from coagulation sludge and its recycle in chemically enhanced primary treatment

An investigation was conducted to study the feasibility of ferric coagulant recovery from chemical sludge and its recycle in chemically enhanced primary treatment (CEPT) to make the process more cost-effective, as well as reduce sludge volume. The optimum conditions and efficiency of the acidification for ferric coagulant recovery from coagulation sludge were investigated. Experimental results showed that the recovered coagulants can be used in CEPT and the pollutants removal efficiency is similar to that of fresh coagulant, and for some aspects the effect of recovered coagulants is better than that of fresh ones, such as turbidity removal. Although some substances will be enriched during recycle, they have little effect on treated wastewater quality. Acidification condition also had significant influence on reduction of sludge volume. The efficiency of coagulant recovery had a linear relationship with sludge reduction. Experiments verify that it would be a sustainable and cost-effective way to recover ferric coagulant from coagulation sludge in water treatment and chemical wastewater treatment, and then recycle it to CEPT, as well as reduce sludge volume.

Removal effect of Cr (VI) by adsorbent made from sewage sludge.

Adsorbent made from sewage sludge is used to remove the Cr (VI) in wastewater. In this paper, the adsorption capacity, adsorption mechanism and regeneration of the adsorbent are studied. A systematic research is carried out to investigate the influence of adsorption capacities in various conditions, such as contact time, pH and initial dosage of adsorbent. The results show that: the equilibrium time is 6 h; the optimal pH is 2.5. The adsorption capacity increases as the initial concentration increase and as the dosage of activated carbon decrease. The data of adsorption capacity are more fit in Langmuir isotherms. The adsorption follows a pseudo-second-order kinetic model perfectly. From this research, the adsorption rate controlling step is film diffusion when the Cr (VI) concentration is low; otherwise, the adsorption rate controlling step is the diffusion among particles. The results of regeneration of saturated adsorbent show that the saturated adsorbent can be perfectly regenerated using alkali treatment. The regeneration ratio of the saturated adsorbent can reach more than 90% with proper concentration of alkali.

A new application of sewage sludge utilization-lightweight aggregate (LWA)

Lots of sewage sludge are generated each year as more wastewater treatment plants appeared in nowadays. How to disposal and utilize sewage sludge has become an urgent problem need to solved. The imposition of more stringent regulations about disposal and utilization of sewage sludge caused some of the traditional methods have been limited, so prompted a drive for alternative uses for sewage sludge. Many researchers have recognized sewage sludge as a resource with much potential for beneficial reuse other than direct disposal. Because the silicon and aluminum-rich characteristics, the dried sludge also exhibits significant specific surface area and cation exchange capacity. Therefore production of lightweight aggregate using dried sludge is a new effective approach for disposal of sludge. This paper seeks to review the published research in this field: it covers the means of production, the characteristics and the potential applications of LWA made from sewage sludge and other waste.

Review on biosorption of heavy metals by activated sludge

The occurrence of heavy metals in our water resources is of continued concern for the health and safety of consuming public. The existing conventional water treatment plants may only partially remove heavy metals, a large fraction of the metals are released to the aquatic environment. Recently, activated sludge emerged as an eco-friendly bioadsorbent, is effective and low cost material option on the removal of hevy metals. This paper discusses the various parameters effected biosorption of heavy metals, such as temperature, pH, biomass concentration, concentrations of initial metal and other factors, etc.. In particular, the removal mechanism is emphasized because of its importance in understanding the reaction between the microorganisms and the metals.

Gasification as a new thermal processes of sewage sludge utilization

Disposal of wastewater treatment sludge is a pressing environmental problem in nowadays, which is aggravated by its accumulation around the world. The imposition of more stringent legislation governing the disposal and utilization of sewage sludge, coupled with the growth in its generation and the loss of traditionally accepted disposal routes, has prompted a drive for alternative uses for sewage sludge. Considering the chemical composition of sludge, some new thermal processes of treatment have recently been considered by researchers. Thermal gasification is one innovative method that could be of significant interest. This paper seeks to review the published research in this field: it covers the characteristics of sewage sludge, the principle of gasification; the applications of sewage sludge in gasification process; the tar elimination and fate of heavy metals in biomass gasification processes.

Advance in microbiology and application of anammox bacteria

The traditional nitrogen removal processes do not meet increasingly stringent discharge standards and sustainable demands. A novel, economical and efficient process was originally discovered in a denitrifying pilot plant reactor, namely anaerobic ammonia oxidation. Some significant advantages make the anammox be a milestone in the field of wastewater treatment and attract much attention, such as low biomass yield and cost. In this paper, the physiological properties, molecular techniques, reaction mechanism of the anammox bacteria and the practical applications are summarized in briefly.