Xiaochen Xu

Removal of COD, phenols and ammonium from Lurgi coal gasification wastewater using A2O-MBR system

As a typical industrial wastewater, coal gasification wastewater has poor biodegradability and high toxicity. In this paper, a laboratory-scale anaerobic-anoxic-oxic membrane reactor (A(2)O-MBR) system was developed to investigate the treatment ability of coal gasification wastewater. The removal capacity of each pollutants used in this system were determined at different hydraulic residence times (HRT) and mixed liquor recycle ratios (R). The experimental results showed that this system could effectively deal with COD and phenol removal and remain in a stable level when the operational parameters altered, while the nitrification was sensitive to operational conditions. The best performance was obtained at HRT of 48 h and R of 3. The maximum removal efficiencies of COD, NH(4)(+)-N and phenols were 97.4%, 92.8% and 99.7%, with final concentrations in the effluent of 71 mg/L, 9.6 mg/L and 3 mg/L, respectively. Organics degradation and transformation were analyzed by GC/MS and it was found that anaerobic process played an important role in degradation of refractory compounds.

Using graphene oxide to enhance the activity of anammox bacteria for nitrogen removal

Graphene oxide (GO) was applied in this study to enhance the activity of anaerobic ammonium oxidation (anammox) bacteria for nitrogen removal. A GO dose-dependent effect on anammox bacteria was observed through batch tests. The results showed that the activity increased as the GO dose was varied within 0.05-0.1gL(-1). A maximum 10.26% increase of anaerobic ammonium oxidizing activity was achieved at 0.1gL(-1) GO. Analysis of extracellular polymeric substances (EPS) indicated that the highest carbohydrate, protein, and total EPS contents (42.5, 125.7, and 168.2mg (g volatile suspended solids)(-1), respectively) were obtained with 0.1gL(-1) GO. Appropriate GO dose stimulated EPS production to promote the activity of anammox bacteria. Transmission electron microscopy showed the large surface area of GO benefited cell attachment. These findings proved that the application of GO was an effective approach to enhancing the activity of anammox bacteria.

Anaerobic fermentation of biogas liquid pretreated maize straw by rumen microorganisms in vitro.

This study intended to investigate the effect of pretreatment of maize straw with biogas liquid on followed fermentation by rumen microorganisms in vitro. The multiple effects including treated time, temperature and dosage of biogas liquid in pretreatment on the followed fermentation performance were analyzed by orthogonal array. The optimum conditions of pretreatment were 9days, 25°C and 50% (v/w) dosage of biogas liquid, which were indicated by the corresponding crystallinity index, dry matter digestibility (DMD) and acetate limiting-step concentration were 57.5%, 73.76% and 1756mg/L, respectively. The ordering sequence of the influential factors for pretreatment was treated time > temperature > dosage of biogas liquid. The results of fermentation showed that the maize straw pretreated by biogas liquid was an efficient and economic pretreatment method of maize straw.

Highly antifouling and antibacterial performance of poly (vinylidene fluoride) ultrafiltration membranes blending with copper oxide and graphene oxide nanofillers for effective wastewater treatment

Innovation and effective wastewater treatment technology is still in great demand given the emerging contaminants frequently spotted from the aqueous environment. By blending with poly (vinylidene fluoride) (PVDF), the strong hydrophilic graphene oxide (GO) and antibacterial copper oxide (CuxO) were used as nanofillers to develop the novel, highly antifouling composite membranes via phase inversion process in our latest work. The existence and dispersion of GO and CuxO posed a significant role on morphologies, structures, surface composition and hydrophilicity of the developed composite membranes, confirmed by SEM, TEM, FTIR and XPS in depth characterization. The SEM images showed that the modified membranes presented a lower resistant structure with developed finger-like macrovoids and thin-walled even interconnected sponge-like pores after adding nanofillers, much encouraging membrane permeation. The XPS results revealed that CuxO contained Cu2O and CuO in the developed membrane and the Cu2O nanoparticles were dominant accounting for about 79.3%; thus the modified membrane specifically exhibited an efficient antibacterial capacity. Due to the hydrophilic and bactericidal membrane surface, the composite membranes demonstrated an excellent antifouling performance, including higher flux recovery rate, more resistant against accumulated contaminants and lower filtration resistance, especially lower irreversible resistance. The antifouling property, especially anti-irreversible fouling, was significantly improved, showing a significant engineering potential.

Selective inhibition of nitrite oxidation by chlorate dosing in aerobic granules.

Partial nitrification was successfully achieved with addition of 5mM KClO(3) in the aerobic granules system. Batch tests demonstrated that KClO(3) selectively inhibited nitrite-oxidizing bacteria (NOB) but not ammonia-oxidizing bacteria (AOB). During stable partial nitrification, the influent pH was kept at 7.8-8.2, while the DO and temperature were not controlled in the SBR. When the NH(4)-N and COD levels were kept at 100mg/l and 400mg/l in the influent, the NH(4)-N and COD removal efficiencies reached 98.93% and 78.65%, respectively. The NO(2)-N accounted for 92.95% of the NO(χ)-N (NO(2)-N+NO(3)-N) in the effluent. Furthermore, about 90% of the chlorate was reduced to nontoxic chloride, thus it would not cause environmental problem. SEM showed that the main composition of the aerobic granules was bacilli and coccus bacteria. FISH analysis revealed that AOB became the dominant nitrifying bacteria, whereas NOB were detected only in low abundance. Chlorate could be used to control the development and maintenance of aerobic granules sludge for partial nitrification.

Wet air oxidation of pretreatment of pharmaceutical wastewater by Cu2+ and [PxWmOy]q- co-catalyst system.

This study concentrates on the pretreatment of real wastewater using catalytic wet air oxidation (CWAO). WO(3-) and PO(4)(3-) contained in fosfomycin pharmaceutical wastewater (FPW) and Cu(2+) contained in berberine pharmaceutical wastewater (BPW) were studied as CWAO influent. Mixture of this two streams were reused to form Cu(2+) and [P(x)W(m)O(y)](q-), namely polyoxometalates (POMs) as co-catalyst system to treat themselves. Experiments were conducted to investigate the effects of the initial oxygen pressure and temperature on the COD (chemical oxygen demand), TOC (total organic carbon) removal and biodegradable enhancement, it was discovered that over 40% of COD and TOC removal can be easily realized in an hour of WAO oxidation at 523 K, 1.4 MPa. The BOD(5)/COD (BOD(5), biochemical oxygen demand in 5 days) of this two pharmaceutical mixture ascended from nonexistent to maximum 0.41 depends on the optimal FPW:BPW volume ratio 4:1, to compose POM co-catalyst system. Organic pollutants were incompletely oxidized to propionic acid and other intermediates. Some properties (e.g., TGA, IR, XRF) of POM catalyst separated from effluent, were obtained to provide additional information.

A pilot-scale study on the start-up of partial nitrification-anammox process for anaerobic sludge digester liquor treatment

Treatment of sludge digester liquor was successfully accomplished using a pilot-scale partial nitrification-anammox (PN/A) reactor with a nitrogen removal rate (NRR) of 1.23kgN/m3/d. A stable and efficient PN process was attained by controlling the concentration of free ammonia (0.7-8.4mg/L) and free nitrous acid (0.02-1.0mg/L). The application of hydroxylamine played a vital role in the reactivation of anammox bacteria. The bacteria exhibited improved granule properties at a specific input power between 0.065 and 0.097kW/m3, and achieved a specific anammox activity (SAA) of 1.01kgN/kgVSS/d on day 148. From day 0 to 120, the heme c content in the granules increased from 0.42±0.1 to 5.77±1.0µmol/gVSS, with a corresponding increase in NRRs and SAAs. High-throughput sequencing techniques revealed that the dominant anammox bacterial genus was Candidatus Brocadia. These conclusions provide valuable information for the full-scale treatment of sludge digester liquor.

The development of a reverse anammox sequencing partial nitrification process for simultaneous nitrogen and COD removal from wastewater

In order to achieve simultaneous removal of nitrogenous and organic pollutants, a novel reverse anammox-partial nitrification nitrogen removal process was developed. During steady operation, the maximum nitrogen and COD (chemical oxygen demand) removal efficiencies were over 90%, with influent NH4(+)-N and COD concentrations of 300 and 100mgL(-1). The optimum recycle ratio of Membrane bioreactor (MBR for partial nitrification) and fixed bed reactor (anammox) for this process was recommended as 3 due to increasingly larger recycle ratio caused slight increase in TN (total nitrogen) removal efficiency. Additionally, the steady nitrogen removal rate was obtained at 0.92-1.03kgNm(-3)day(-1). Considering its great potential in nitrogen removal, this reverse process will be revealing for the study of anammox technique.

Comparison of the characteristics of anammox granules of different sizes

The physical properties and performance of anaerobic ammonium oxidation (anammox) granules of different sizes (0.5 ∼ 1.0 mm, 1.0 ∼ 1.5 mm, and above 1.5 mm) have been investigated. The values of the settling velocity increased with increasing size of the granules. There was no significant difference in metal contents among granules of different sizes, in which calcium, magnesium and iron were the predominant ions. Different start-up periods showed that larger granules were better able to resist adverse impacts and their activities could quickly be recovered. The specific activities of granules of different sizes were 0.55, 0.62, and 0.52 g N/ (g/VSS/day), respectively, which implied the activity of 1.0 ∼ 1.5 mm granules was the highest. Larger anammox granules were better able to resist temperature shock and nitrogenous shock loading. However, larger granules were also shown to contain bigger gas tunnels and interior hollows, which decrease the stability of anammox granules. With the comprehensive consideration of bacteria activity, granule stability and shock resistance capacity, the properties of granules within the size range of 1.0 ∼ 1.5 mm were found superior to others in this study.

Influence of inlet radius on Stokes flow in a circular tube via the Hamiltonian systematic method

This paper presents a new semianalytical method, Hamiltonian systematic method, for solving axisymmetric problems of Stokes flow. In the system, nonzero-eigenvalue solutions can describe local effect near the boundary and therefore the influence of inlet radius on the flow can be investigated. A rule of minimal entrance length is discussed on the basis of the criteria which are defined by axial flow deviating from the full developed (Hagen–Poseuille) flow. Numerical results show that the entrance length is related to the inlet radius, and there is one minimal point on the relationship curve, namely, there is one minimal entrance length. Besides, pressures have the characteristic too and the minimal point is same. The method can also be generalized to other fields.