Tianwei Hao

A review of biological sulfate conversions in wastewater treatment

Treatment of waters contaminated with sulfur containing compounds (S) resulting from seawater intrusion, the use of seawater (e.g. seawater flushing, cooling) and industrial processes has become a challenging issue since around two thirds of the worlds population live within 150 km of the coast. In the past, research has produced a number of bioengineered systems for remediation of industrial sulfate containing sewage and sulfur contaminated groundwater utilizing sulfate reducing bacteria (SRB). The majority of these studies are specific with SRB only or focusing on the microbiology rather than the engineered application. In this review, existing sulfate based biotechnologies and new approaches for sulfate contaminated waters treatment are discussed. The sulfur cycle connects with carbon, nitrogen and phosphorus cycles, thus a new platform of sulfur based biotechnologies incorporating sulfur cycle with other cycles can be developed, for the removal of sulfate and other pollutants (e.g. carbon, nitrogen, phosphorus and metal) from wastewaters. All possible electron donors for sulfate reduction are summarized for further understanding of the S related biotechnologies including rates and benefits/drawbacks of each electron donor. A review of known SRB and their environmental preferences with regard to bioreactor operational parameters (e.g. pH, temperature, salinity etc.) shed light on the optimization of sulfur conversion-based biotechnologies. This review not only summarizes information from the current sulfur conversion-based biotechnologies for further optimization and understanding, but also offers new directions for sulfur related biotechnology development.

Impact of Influent COD/N Ratio on Disintegration of Aerobic Granular Sludge

Disintegration of aerobic granular sludge (AGS) is a challenging issue in the long-term operation of an AGS system. Chemical oxygen demand (COD)-to-nitrogen (N) ratio (COD/N), often variable in industrial wastewaters, could be a destabilizing factor causing granule disintegration. This study investigates the impact of this ratio on AGS disintegration and identifies the key causes, through close monitoring of AGS changes in its physical and chemical characteristics, microbial community and treatment performance. For specific comparison, two lab-scale air-lift type sequencing batch reactors, one for aerobic granular and the other for flocculent sludge, were operated in parallel with three COD/N ratios (4, 2, 1) applied in the influent of each reactor. The decreased COD/N ratios of 2 and 1 strongly influenced the stability of AGS with regard to physical properties and nitrification efficiency, leading to AGS disintegration when the ratio was decreased to 1. Comparatively the flocculent sludge maintained relatively stable structure and nitrification efficiency under all tested COD/N ratios. The lowest COD/N ratio resulted in a large microbial community shift and extracellular polymeric substances (EPS) reduction in both flocculent and granular sludges. The disintegration of AGS was associated with two possible causes: 1) reduction in net tyrosine production in the EPS and 2) a major microbial community shift including reduction in filamentous bacteria leading to the collapse of granule structure.

Characterization of sulfate-reducing granular sludge in the SANI® process

Hong Kong practices seawater toilet flushing covering 80% of the population. A sulfur cycle-based biological nitrogen removal process, the Sulfate reduction, Autotrophic denitrification and Nitrification Integrated (SANI(®)) process, had been developed to close the loop between the hybrid water supply and saline sewage treatment. To enhance this novel process, granulation of a Sulfate-Reducing Up-flow Sludge Bed (SRUSB) reactor has recently been conducted for organic removal and provision of electron donors (sulfide) for subsequent autotrophic denitrification, with a view to minimizing footprint and maximizing operation resilience. This further study was focused on the biological and physicochemical characteristics of the granular sulfate-reducing sludge. A lab-scale SRUSB reactor seeded with anaerobic digester sludge was operated with synthetic saline sewage for 368 days. At 1 h nominal hydraulic retention time (HRT) and 6.4 kg COD/m(3)-d organic loading rate, the SRUSB reactor achieved 90% COD and 75% sulfate removal efficiencies. Granular sludge was observed within 30 days, and became stable after 4 months of operation with diameters of 400-500 μm, SVI5 of 30 ml/g, and extracellular polymeric substances of 23 mg carbohydrate/g VSS. Fluorescence in situ hybridization (FISH) analysis revealed that the granules were enriched with abundant sulfate-reducing bacteria (SRB) as compared with the seeding sludge. Pyrosequencing analysis of the 16S rRNA gene in the sulfate-reducing granules on day 90 indicated that the microbial community consisted of a diverse SRB genera, namely Desulfobulbus (18.1%), Desulfobacter (13.6%), Desulfomicrobium (5.6%), Desulfosarcina (0.73%) and Desulfovibrio (0.6%), accounting for 38.6% of total operational taxonomic units at genera level, with no methanogens detected. The microbial population and physicochemical properties of the granules well explained the excellent performance of the granular SRUSB reactor.

Seawater-based Wastewater Accelerates Development of Aerobic Granular Sludge: A Laboratory Proof-of-concept

This study aimed to develop an aerobic granular sludge process for the efficient treatment of highly saline wastewater and understand the granulation process in a seawater-based multi-ion matrix. Five identical sequencing batch airlift reactors (SBARs) are used to treat synthetic saline sewage with different proportions of real seawater (0%-100%). The results confirm that aerobic granular sludge can be successfully developed with various proportions of seawater up to 100% and show that seawater not only significantly accelerates granulation but also generates stronger granular structures than does freshwater. The increased presence of gel-forming alginate-like exopolysaccharides in the granules explains why a greater proportion of seawater leads to higher density and improves the cohesive strength of the granules. SEM-EDX analysis further revealed substantial presence of both Ca2+ and Mg2+ phosphate in the granule core as well as in the outer layers providing extra bridging forces in addition to alginate-like exopolysaccharides for accelerating the granule formation and maintaining the structure. It is hoped that this work could explore another approach for saline sewage treatment and bring some clues for the mystery of granulation mechanism.

Alkaline textile wastewater biotreatment: A sulfate-reducing granular sludge based lab-scale study

In this study the feasibility of treating dyeing wastewater with sulfate reducing granular sludge was explored, focusing on decolorization/degradation of azo dye (Procion Red HE-7B) and the performance of microbial consortia under alkaline conditions (pH=11). Efficiency of HE-7B degradation was influenced strongly by the chemical oxygen demand (COD) concentration which was examined in the range of 500-3000mg/L. COD removal efficiency was reduced at high COD concentration, while specific removal rate was enhanced to 17.5 mg-COD/gVSSh-1. HE-7B removal was also improved at higher organic strength with more than 90% removal efficiency and a first-rate removal constant of 5.57h-1 for dye degradation. Three dye-degradation metabolites were identified by HPLC-MS. The granular structure provided enhanced removal performance for HE-7B and COD in comparison to a near-identical floc SRB system and the key functional organisms were identified by high throughput sequencing. This study demonstrates an example of a niche application where SRB granules can be applied for high efficient and cost-effective treatment of a wastewater under adverse environmental conditions.

Effect of L-tyrosine on aerobic sludge granulation and its stability

Aerobic sludge granulation and its stability remain challenging in applications. Tyrosine, a compound in extracellular polymeric substances (EPSs) extracted from sludge, is reported to be closely associated with sludge granulation and its stability. In order to confirm this, this study investigated the effect of L-tyrosine on granulation and disintegration of granular sludge in two identical sequencing airlift bioreactors (SABRs): one dosed with L-tyrosine (6 mg L−1) and the other without dosing. Changes in the physiochemical and biological properties of the aerobic granular sludge (AGS) and organic and nitrogen removal in both reactors operated under different ratios of chemical oxygen demand (COD) to nitrogen were closely monitored for 120 days. The L-tyrosine dosing shortened full granulation of AGS by 1 month. Disintegration of the granules and deterioration in the COD and nitrogen removal capability were not observed in the L-tyrosine dosed reactor even when the ratio of COD/N in the influent was reduced from 4 to 1 unlike the control reactor. This clearly confirmed the contribution of L-tyrosine in promoting AGS granulation and its stability. Both the enrichment of quorum sensing auto-inducer relating bacteria genera (21%) and the stable production of EPS were suggested as main reasons for the positive effect of L-tyrosine on the granulation and stability of AGS.

Phosphorus release and uptake during start-up of a covered and non-aerated sequencing batch reactor with separate feeding of VFA and sulfate

This study explored a sulfur cycle-associated biological phosphorus (P) removal process in a covered and non-aerated sequencing batch reactor (SBR) fed with volatile fatty acid (VFA) and sulfate separately. During the 60-day start-up, both phosphate release and uptake rates increased, while poly-phosphate cyclically increased and decreased accordingly. The P-release and P-uptake rates were associated with VFA uptake and sulfate reduction. The average ratio of potassium to phosphate during the P-uptake and P-release was also determined to be 0.29-0.31 mol K/mol P, which is close to a reported value (0.33) for biological phosphorus removal. All this evidence confirmed there was biological P removal in this reactor, in which metabolism could be different from conventional biological P removal.

Enzymatic nitrous oxide emissions from wastewater treatment

Nitrous oxide (N2O), a potent greenhouse gas, is emitted during nitrogen removal in wastewater treatment, significantly contributing to greenhouse effect. Nitrogen removal generally involves nitrification and denitrification catalyzed by specific enzymes. N2O production and consumption vary considerably in response to specific enzyme-catalyzed nitrogen imbalances, but the mechanisms are not yet completely understood. Studying the regulation of related enzymes’ activity is essential to minimize N2O emissions during wastewater treatment. This paper aims to review the poorly understood related enzymes that most commonly involved in producing and consuming N2O in terms of their nature, structure and catalytic mechanisms. The pathways of N2O emission during wastewater treatment are briefly introduced. The key environmental factors influencing N2O emission through regulatory enzymes are summarized and the enzyme-based mechanisms are revealed. Several enzymebased techniques for mitigating N2O emissions directly or indirectly are proposed. Finally, areas for further research on N2O release during wastewater treatment are discussed.

Using sulfite pretreatment to improve the biodegradability of waste activated sludge

This study presents a novel strategy to improve the biodegradability of waste activated sludge (WAS) based on sulfite pretreatment. Experiments were conducted to demonstrate the effects of sulfite on the WAS and its biodegradability by sulfite pretreatment. The results show that the concentration of the released substrate in the sulfite (0.2–0.48 g S L−1) pretreated WAS increased 2–5 times after 12–36 h, at a pH of 5–7, compared with the WAS without pretreatment. The concentration of soluble chemical oxygen demand (SCOD) produced had a strong correlation with the concentration of sulphurous acid (H2SO3), suggesting that H2SO3 may directly cause the lysis of microorganisms in WAS. Biogenic sulfide production (BSP) was applied for the assessment of anaerobic biodegradability. The results indicated that the biodegradability of the WAS after sulfite pretreatment improved by approximately 51% compared with the control system. Moreover, the rate of sulfate/sulfite reduction in the Experimental reactor was 1.62 times higher than the value in the Control reactor, thereby further confirming the improvement observed in the biodegradability of the sulfite pretreated WAS. The released substrates and produced sulfide can be further applied as renewable sources of energy.

A novel approach to quantifying elemental sulfur (S0) in environmental samples

The quantification of elemental sulfur (S0) is an important part of monitoring and controlling sulfur-involving processes. Existing methods of S0 detection either require significant time or involve the use of toxic chemicals. We have developed and validated a new method to determine S0 in environmental samples using calorimeter-ion chromatography (IC), in which S0 is fully oxidized to sulfur trioxide (SO3) with pure oxygen at 20 atm in a calorimeter. The resulting SO3 is then absorbed by a sodium bicarbonate (NaHCO3) solution and analyzed using IC. To verify this method, standard samples with various sulfur contents (5-200 mg S), possible interfering substances (SO42-, SO32-, S2O32- and S2-), and mixed environmental samples were tested and compared. The high correlation of R2 = 0.999 between the examined and theoretical values was obtained with a high recovery rate of ≥95% and a low relative standard deviation (RSD) of ≤1%. Samples containing at least 25 mg of S0 were accurately measured (recovery error < 5%). Thiosulfate was identified as the main interfering substance, and pretreatment was needed to eliminate it. This new method is more efficient, cost-effective, easier to operate, and more secure and accurate than existing methods.