Lixiang Zhou

Isolation and nitrogen removal characteristics of an aerobic heterotrophic nitrifying-denitrifying bacterium, Bacillus subtilis A1

Bacterium A1, isolated to enhance nitrogen removal from ammonium-rich wastewater in situ, exhibited an amazing ability to convert ammonium to gaseous nitrogen compounds under fully aerobic conditions, while growing autotrophically or heterotrophically. A1 was identified as Bacillus subtilis by morphological and physiological characteristics, and phylogenetic analysis of its 16S rDNA gene sequence. Nitrogen removal by A1 was analyzed in relation to the ammonium concentration, presence of organic carbon, carbon source, and carbon-to-nitrogen ratio (C/N). The nitrogen balance during 120 h of autotrophic growth in the presence of 104.12±1.27 mg/L NH4+N showed that 20.4±2.7% of NH4+N was removed as gaseous nitrogen compounds, and A1 removed 58.4±4.3% of NH4+N within 60 h of growth in acetate medium at a C/N of 6. A mean ammonium removal rate of 3.52 mg NH4+N/(L h) was achieved in an open wastewater system, indicating great potential of A1 for future full-scale applications.

New approach to studies of heavy metal redistribution in soil

Abstract The bioavailability and mobility of heavy metals in soils is dependent upon redistribution processes between solution and solid phases and among solid-phase components. This paper reviews the definitions and applications of two newly developed parameters, the redistribution index and the reduced partitioning parameter, in quantifying redistribution processes of heavy metals in contaminated soils. The redistribution index depicts the removal/attainment of metal-contaminated soils from/to the fractional distribution pattern characteristic of non-amended soils, while the reduced partitioning parameter quantifies the relative binding intensity of heavy metals in soils. Over time, metal salt-spiked and sludge-amended soils approached the fractional distribution pattern of non-amended soils. The rates of redistribution of metals and their binding intensity in soils were affected by the metal species, loading levels and soil properties. Metals in contaminated soils at low loading levels approach the fractional distribution pattern of non-amended soil more rapidly than those at high loading levels. The sequence order of approach by metals to the fractional distribution pattern of non-amended soil was: Cd>Cu>Ni=Zn>Cr. In both non-amended and contaminated soils, Cr had the highest binding intensity, Cd the lowest, and Cu, Ni and Zn, intermediate values. In addition to our own data, primarily on metal salt-spiked soils, these two indices are also used to evaluate redistribution processes of heavy metals in sewage sludge-amended soils from other published reports.

Effect of carbon source, C/N ratio, nitrate and dissolved oxygen concentration on nitrite and ammonium production from denitrification process by Pseudomonas stutzeri D6

Pseudomonas stutzeri D6, selectively isolated from activated sludge was used to study NO(2)(-) and NH(4)(+) production from denitrification processes. Changes in carbon type, C/N ratio and oxygen concentration significantly influenced the magnitude of NO(2)(-) and NH(4)(+) accumulation through denitrification. D6 showed a preference for citrate and acetate, which led to the largest quantity of nitrate reduced and which were exhausted most rapidly, with minimal intermediate products accumulation. It is found that at higher initial organic carbon concentration or for directly metabolic carbon type more complete denitrification could be obtained as a result of increase of the oxygen consumption rate by substrate stimulation. The higher the oxygen concentration in the culture was, the higher the intermediate products concentration became. The experiment showed that NO(2)(-) and NH(4)(+) production was only slightly influenced by nitrate concentration. Biological nitrogen removal systems should be optimized to promote complete denitrification to minimize NO(2)(-) and NH(4)(+) accumulation.

Adsorptive removal of As(III) by biogenic schwertmannite from simulated As-contaminated groundwater

This study investigates synthesis of biogenic schwertmannite by Acidithiobacillus ferrooxidans and its role and mechanism in adsorption of As(III) from water. Results indicate that schwertmannite particles formed through oxidation of ferrous sulfate by A. ferrooxidans cells for different times vary greatly in size and in morphology. The hedge-hog like schwertmannite formed after reaction for 72h are aggregative spheroid particles with a diameter of approximately 2.5μm and its chemical formula can be expressed as Fe(8)O(8)(OH)(4.42)(SO(4))(1.79). Batche studies show that both Freundlich and Langmuir model are suitable for describing the adsorption behavior of As(III) on schwertmannite at pH 7.5 and As(III) in simulated groundwater can be effectively removed by biogenic schwertmannite with a maximum adsorption capacity of 113.9mg As(III) g(-1) and the optimal pH is in the range of 7-10. The arsenic removal is hardly affected by the competing anions often observed in groundwater unless the mole concentration of PO(4)(3-) and SO(4)(2-) in groundwater are 75 or 750 times higher than As(III), respectively. The mechanism of As(III) adsorption on biogenic schwertmannite involves ligand exchanges between arsenic species and surface hydroxyl group and sulfate. In addition, experiments show that As(III)-sorbed biogenic schwertmannite aged in deionized water at 25°C exhibits no mineralogy phase changes even after ageing at pH 6.0 and 8.5 for 90d.

Improvement of sludge dewaterability and removal of sludge-borne metals by bioleaching at optimum pH.

Bio-acidification caused by bio-oxidation of energy substances during bioleaching is widely known to play an important role in improving sludge-borne metals removal. Here we report that bioleaching also drastically enhances sludge dewaterability in a suitable pH level. To obtain the optimum initial concentrations of energy substances and pH values for sludge dewaterability during bioleaching, bio-oxidation of Fe(2+) and S(0) under co-inoculation with Acidithiobacillus thiooxidans TS6 and Acidothiobacillus ferrooxidans LX5 and their effects on sludge dewaterability and metals removal during sludge bioleaching were investigated. Results indicated that the dosage of energy substances with 2g/L S(0) and 2g/L Fe(2+) could obtain bio-oxidation efficiencies of up to 100% for Fe(2+) and 50% for S(0) and were the optimal dosages for sludge bioleaching. The removal efficiencies of sludge-borne Cu and Cr could reach above 85% and 40%, respectively, and capillary suction time (CST) of bioleached sludge decreased to as low as ∼10s from initial 48.9s for fresh sludge when sludge pH declined to ∼2.4 through bioleaching. These results confirm the potential of bioleaching as a novel method for improving sludge dewaterability as well as removal of metals.

Enhancing sewage sludge dewaterability by bioleaching approach with comparison to other physical and chemical conditioning methods.

The sewage sludge conditioning process is critical to improve the sludge dewaterability prior to mechanical dewatering. Traditionally, sludge is conditioned by physical or chemical approaches, mostly with the addition of inorganic or organic chemicals. Here we report that bioleaching, an efficient and economical microbial method for the removal of sludge-borne heavy metals, also plays a significant role in enhancing sludge dewaterability. The effects of bioleaching and physical or chemical approaches on sludge dewaterability were compared. The conditioning result of bioleaching by Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans on sludge dewatering was investigated and compared with the effects of hydrothermal (121 degrees C for 2 hr), microwave (1050 W for 50 sec), ultrasonic (250 W for 2 min), and chemical conditioning (24% ferric chloride and 68% calcium oxide; dry basis). The results show that the specific resistance to filtration (SRF) or capillary suction time (CST) of sludge is decreased by 93.1% or 74.1%, respectively, after fresh sludge is conditioned by bioleaching, which is similar to chemical conditioning treatment with ferric chloride and calcium oxide but much more effective than other conditioning approaches including hydrothermal, microwave, and ultrasonic conditioning. Furthermore, after sludge dewatering, bioleached sludge filtrate contains the lowest concentrations of chroma (18 times), COD (542 mg/L), total N (TN, 300 mg/L), NH4(+)-N (208 mg/L), and total P (TP, 2 mg/L) while the hydrothermal process resulted in the highest concentration of chroma (660 times), COD (18,155 mg/L), TN (472 mg/L), NH4(+)-N (381 mg/L), and TP (191 mg/L) among these selected conditioning methods. Moreover, unlike chemical conditioning, sludge bioleaching does not result in a significant reduction of organic matter, TN, and TP in the resulting dewatered sludge cake. Therefore, considering sludge dewaterability and the chemical properties of sludge filtrate and resulting dewatered sludge cakes, bioleaching has potential as an approach for improving sludge dewaterability and reducing the cost of subsequent reutilization or disposal of dewatered sludge.

Heterotrophic microorganism Rhodotorula mucilaginosa R30 improves tannery sludge bioleaching through elevating dissolved CO2 and extracellular polymeric substances levels in bioleach solution as well as scavenging toxic DOM to Acidithiobacillus species.

The introduction of acid-tolerant heterotrophic microorganisms into sludge bioleaching systems has been proven effective in improving sludge bioleaching processes, and such positive effect is mainly attributed to the biodegradation of low molecular weight organic acids or sludge dissolved organic matter (DOM) toxic to Acidithiobacillus species by the heterotrophic microorganisms introduced. Here we report that elevated dissolved CO(2) concentration and resulting extracellular polymeric substances (EPS) in bioleach solution due to the incorporation of heterotrophic microorganisms also play important roles in improving sludge bioleaching. It was found that in tannery sludge bioleaching system coinoculated with Rhodotorula mucilaginosa R30 and Acidithiobacillus species, dissolved CO(2) concentration in bioleach solution can be elevated from 0.23-0.54 mg/L to 0.76-1.01 mg/L compared to the control inoculated only with Acidithiobacillus species. Correspondingly, the distinct degradation of sludge DOM was also observed in this experiment. It was experimentally demonstrated that the accumulation of CO(2) did greatly enhance the growth of Acidithiobacillus thiooxidans and the decrease rate of pH in the medium. In addition, EPS derived from R. mucilaginosa R30 could bind readily Fe(3+) in bioleach solution with maximum binding capacity (MBC) of 0.82 mg Fe(3+) by per mg DOC of EPS secreted and the oxidization activity of EPS-bound Fe(3+) was decreased but not totally inhibited, indicating that the formation of soluble EPS-Fe(III) complexes enhances, to a certain extent, bioleaching efficiency due to maintaining Fe(3+) level in solution by inhibiting Fe precipitation occurrence.

Enhancement of the dewaterability of sludge during bioleaching mainly controlled by microbial quantity change and the decrease of slime extracellular polymeric substances content

Contribution rates of factors controlling sludge dewaterability during bioleaching, such as sludge pH, microbial quantity, extracellular polymeric substances (EPS), etc., were investigated in this study. Results showed that the dewaterability of bioleached sludge was jointly enhanced by the growth of Acidithiobacillus sp., the increase of Fe(3+) concentration, the decreases of sludge pH, heterotrophic microorganism quantity change, and the decreases of EPS and bound water contents. Ridge regression analysis further revealed that the contribution rates of microbial quantity change, bound water content and slime EPS content on sludge dewaterability enhancement were 32.50%, 24.24%, and 22.37%, respectively, all of which are dominant factors. Therefore, the enhancement of sludge dewaterability was mainly controlled by microbial quantity change and the decrease of bound water and slime EPS contents during bioleaching.

Influences of Extracellular Polymeric Substances on the Dewaterability of Sewage Sludge during Bioleaching

Extracellular polymeric substances (EPS) play important roles in regulating the dewaterability of sludge. This study sought to elucidate the influence of EPS on the dewaterability of sludge during bioleaching process. Results showed that, in bioleaching system with the co-inoculation of Acidithiobacillus thiooxidans TS6 and Acidithiobacillus ferrooxidans LX5 (A. t+A. f system), the capillary suction time (CST) of sludge reduced from 255.9 s to 25.45 s within 48 h, which was obviously better than the controls. The correlation analysis between sludge CST and sludge EPS revealed that the sludge EPS significantly impacted the dewaterability of sludge. Sludge CST had correlation with protein content in slime and both protein and polysaccharide contents in TB-EPS and Slime+LB+TB layers, and the decrease of protein content in slime and decreases of both protein and polysaccharide contents in TB-EPS and Slime+LB+TB layers improved sludge dewaterability during sludge bioleaching process. Moreover, the low sludge pH (2.92) and the increasing distribution of Fe in the solid phase were another two factors responsible for the improvement of sludge dewaterability during bioleaching. This study suggested that during sludge bioleaching the growth of Acidithiobacillus species resulted in the decrease of sludge pH, the increasing distribution of Fe in the solid phase, and the decrease of EPS content (mainly including protein and/or polysaccharide) in the slime, TB-EPS, and Slime+LB+TB layers, all of which are helpful for sludge dewaterability enhancement.

Photocatalytic reduction of Cr(VI) by citric and oxalic acids over biogenetic jarosite

In this study, a series of bath experiments were carried out to investigate the photoreduction of Cr(VI) by small molecular weight organic acids (SOAs) over jarosite, a mineral found in acid mine drainage (AMD). The results demonstrated that jarosite or SOAs alone was unable to effectively transform Cr(VI) to Cr(III) even if exposed to an illumination of mimic solar light. However, an addition of jarosite significantly enhanced the reduction of Cr(VI) by SOAs under the same condition. The photocatalytic reduction of Cr(VI) was strongly influenced by pH, the initial concentrations and the structures of SOAs. Of the tested two SOAs, the reaction rates of photocatalytic reduction of Cr(VI) were in the order of oxalic acid>citric acid. The reaction obeyed to zero-order kinetics with respect to Cr(VI) with excess SOAs. A possible mechanism for photoreduction of Cr(VI) by SOAs over jarosite was proposed.