A novel integration of microwave catalytic oxidation and MBBR process and its application in advanced treatment of biologically pretreated Lurgi coal gasification wastewater

Experimental study of microwave-catalytic oxidative degradation of COD in livestock farming effluent by copper-loaded activated carbon

The problem of massive discharge of livestock wastewater is becoming more and more severe, causing irreversible damage to the ecological environment, and how to treat livestock wastewater efficiently and rapidly deserves to be studied in depth. In this work, CuO/granular activated carbon (GAC) loaded catalysts were prepared and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption techniques, and X-ray energy spectroscopy (EDS). The results showed that CuO was successfully attached to the GAC surface with good adsorption performance. The effects of catalyst dosage, H2O2 dosage, initial pH, microwave power and microwave irradiation time in different reaction systems on the degradation efficiency of chemical oxygen demand (COD) in wastewater were investigated, and the orthogonal experiments were used to explore the importance ranking of these factors. The highest degradation rate of COD was found to be enhanced by 12.1% in the reaction system of CuO/GAC, and the initial pH had the greatest effect on the COD removal rate. The combined MW/catalyst/H2O2 method used in this work provided a rapid and effective degradation of COD in wastewater, which can be helpful for reference in other microwave catalytic oxidation studies.

The influence mechanism of DO on the microbial community and carbon source metabolism in two solid carbon source systems

The regulation mechanism of parameters on microorganisms and carbon source metabolism of solid carbon source simultaneous nitrification and denitrification (SND) process is not clear. In this paper, the effects of dissolved oxygen (DO) and biodegradable polymer (BDPs) types ((Polycaprolactone, PCL) and (Polybutylene succinate, PBS)) on treatment performance and microbial characteristics were investigated. The results show that the total nitrogen (TN) removal efficiency of SND process using PBS and PCL as fillers reached 93.02% and 97.28% under optimal parameter of DO 5 mg/L, respectively. The dominant genus with nitrogen removal performance in the PCL carbon source system are Hydrogenophaga and Acidovorax, and the main genus in the PBS system are Acidovorax and unclassified_Comamonadaceae. The co-metabolic network in PCL is more complex and easier to be regulated by DO. The BDPs types mainly affect the co-metabolic network with nodes of Thiothrix and Chryseomicrobium, ultimately leading to changes in the community structure. By comparison, BDPs types have a more significant impact on community structure than DO under low DO conditions (1 and 2 mg/L), but not under high DO condition(5 mg/L). Further, the distribution of functional enzymes may conflict between nitrification and carbon source degradation under high DO condition. Controlling the DO within the range of 2 mg-5 mg can further improve carbon source utilization efficiency.

Can a compact biological system be used for real hydraulic fracturing wastewater treatment?

Hydraulic fracturing wastewater (HFW), a byproduct of hydraulic fracturing oil extraction, contains a complex mixture of oil, aldehydes, and benzene compounds. Efficient and eco-friendly HFW treatment means are critical for the oil extraction industry, particularly in developing countries. In this study, two biological processes namely an anaerobic/anoxic/moving bed biofilm reactor (A²-MBBR) and an A²-MBBR with a microfiltration membrane (A²-MFMBBR) were established, and assessed for the real HFW treatment. Removal efficiencies of chemical oxygen demand (COD) and NH₄⁺-N were over 92% and 95%, respectively, in both processes with a hydraulic retention time of 72 h. The majority of organic compounds in both systems identified by GC-MS were degraded in the anaerobic units. In comparison, A²-MFMBBR demonstrated higher removal efficiencies for oil, total suspended solids, and complex compounds. The average relative abundances of refractory compound degrading bacteria were 43.4% and 51.6% in the A²-MBBR and A²-MFMBBR, respectively, which was consistent with the COD and oil removal, and suggested that the MBR could maintain a high diversity of microorganisms and contribute to deep recalcitrant organics degradation. This study sheds light on the potential of using a compact biological process for the real HFW treatment.

Advances in treatment of coking wastewater - a state of art review

Coking wastewater poses a serious threat to the environment due to the presence of a wide spectrum of refractory substances such as phenolic compounds, polycyclic aromatic hydrocarbons and heterocyclic nitrogenous compounds. These toxic substances are difficult to treat using conventional treatment methods alone. In recent years much attention has been given to the effective treatment of coking wastewater. Thus, this review seeks to provide a brief overview of recent developments that have taken place in the treatment of coking wastewater. In addition, this article addresses the complexity and the problems associated with treatment followed by a discussion on biological methods with special focus on bioaugmentation. As coking wastewater is refractory in nature, some of the studies have been related to improving the biodegradability of wastewater. The final section focuses on the integrated treatment methods that have emerged as the best solution for tackling the highly unmanageable coking wastewater. Attention has also been given to emerging microwave technology which has tremendous potential for treatment of coking wastewater.

Environmental contamination by heterocyclic Polynuclear aromatic hydrocarbons and their microbial degradation

Heterocyclic polynuclear aromatic hydrocarbons (PAHs) have been detected in all environmental matrices at few ppb to several ppm concentrations and they are characterized by high polarity. Some heterocyclic PAHs are mutagenic and carcinogenic to humans and various organisms. Despite being potent environmental pollutants, these compounds have received less attention. This paper focuses on the sources and occurrence of these compounds and their microbial degradation using diverse species of bacteria, fungi, and algae. Complete removal of 1.8 to 2614 mg/L of nitrogen heterocyclic PAH (PANH), 0.27 to 184 mg/L of sulfur heterocyclic PAH (PASH), and 0.6 to 120 mg/L of oxygen heterocyclic PAH (PAOH) compounds by various microbial species was observed between 3 h and 18 days, 8 h to 6 days, and 4 h to 250 h, respectively under aerobic condition. Strategies for enhancing the removal of heterocyclic PAHs from aquatic systems are also discussed along with the challenges.

Two-stage coagulation process for enhanced oil removal from coal chemical wastewater

As a common pretreatment process for coal chemical wastewater, the conventional one-stage coagulation process has the problem of poor removal of small size oil, which will inhibit the subsequent biological treatment. Measures to improve oil removal efficiency based on the development of new coagulants and the addition of composite processes are common in the literature, but two-stage coagulation to improve coagulation efficiency has not been reported to date. Here, we optimized coagulation parameters and compared the oil removal efficiency of two-stage coagulation and one-stage coagulation. Under the same total dosage of coagulant (PAC), the optimum removal of oil in two-stage coagulation was achieved 90% which increased by 11% compared to one-stage process. P10 and P 1 μm were proposed to evaluate the oil removing effect of two-stage coagulation. In addition, SEM scanning was used to conduct flocs analysis and two-stage coagulation process simulation, revealing the principle of the excellent oil removal performance of two-stage coagulation. Finally, coagulant in filter residue was recovered by acidification method and the recovered coagulant was used again in the two-stage coagulation process of coal chemical wastewater. These results suggest that two-stage coagulation is a cost-effective alternative oil removal technique with high energy efficiency and environmental benign. This research may offer helpful insights to develop an advanced oil removal process.

Effective oxidative degradation of coal gasification wastewater by ozonation: A process study

Coal gasification wastewater (CGW) has attracted considerable industrial attention because of its high toxicity and poor biodegradability. Ozonation is a promising process for CGW treatment. In this study, the effects of ozone concentration, pH, and ozonation time on CGW treatment were investigated. The results confirmed that CGW was degraded effectively and that the chemical oxygen demand (COD) was reduced from 1057 to 362 mgL^-1, utilizing 50 mgL^-1 ozone for 90 min. Further, the color of CGW changed from brown to clear and colorless, and the pH decreased from 8.5 to 4.7. Importantly, molds were observed in the oxidized CGW after 14 d at room temperature (23 ± 2 °C), indicating that CGW is significantly biodegradable by ozonation. The CGW components were extracted with three different organic solvents (chloroform, n-hexane, and benzene), and their compositions were analyzed by gas chromatography-mass spectrometry (GC-MS) before and after ozonation. The results proved that considerable amounts of highly toxic refractory compounds in CGW, such as phenolic compounds, polynuclear aromatic hydrocarbons (PAHs), and nitrogenous heterocyclic compounds (NHCs), were degraded to compounds that included olefins, carboxylic acids, and cycloalkanes, or minerals, which are relatively environmentally benign. Moreover, the number of substances in CGW decreased significantly from 127 to 74 after ozonation. Summarily, ozonation is a promising approach for the treatment of highly toxic refractory wastewater, such as CGW.

Overview of the state of the art of processes and technical bottlenecks for coal gasification wastewater treatment

CGWW is major waste stream resulting from a number of activities of the low/medium temperature gasification unit that occurs during the production of natural gas. The resulting effluent contains a broad spectrum of organic and inorganic contaminants and exerts a negative influence on the environment, mainly due to the presence of toxic and refractory compounds. So far, various technologies have been applied for treatment of CGWW, while few reviews are available in the literature. Thus, this review attempts to offer a comprehensive picture about CGWW. An overview about pretreatment, biological and advanced processes for treatment of CGWW is presented, and the degradation mechanism of toxic and refractory pollutants is also elaborated. Technical bottlenecks existing in the operation of coal chemical industries, including foam proliferation, odors and biotoxicity risk, are detailed analyzed. Finally, the prospects of treatment for CGWW are discussed based on the concept of "wastewater is money". The review can be provided as an effective technical support for the construction and operation of coal gasification industries.

Degradation characteristics of two typical N-heterocycles in ozone process: Efficacy, kinetics, pathways, toxicity and its application to real biologically pretreated coal gasification wastewater

Ozonation of pyridine and indole was investigated both in aqueous solution and biologically pretreated coal gasification wastewater (BPCGW). Experimental results showed that the removal of indole was hardly affected by pH value. Direct reaction rate constant of ozone with pyridine increased from 0.18 M^-1 s^-1 (protonated pyridine) to 3.03 M^-1 s^-1 (molecular pyridine), and that with molecular indole was 8.6 × 10⁵ M^-1 s^-1. Seven and five transformation intermediates were observed for pyridine and indole, respectively. Ozonation pathways were proposed as hydroxylation, opening and cleavage of the aromatic ring. It was found that ammonia nitrogen (NH₃N) increased by 3.3 mg L^-1 in ozone process, suggesting the broken of the CN bonds of pyridine, indole and other N-heterocyclic compounds. In terms of biochemical oxygen demand to chemical oxygen demand (BOD₅/COD), toxicity and resazurin dehydrogenase activity (DHA), the biodegradability was improved after ozone treatment, indicating the possibility of ozone combined with biosystem for the treatment of BPCGW. The results of gas chromatograph and mass spectrometry (GC-MS) indicated that primary products during first 10 min might lead to the obstinate toxicity, which was further proved by US Environmental Protection Agency (US-EPA) test. This study would assist in obtaining a better understanding of the application of ozonation pretreatment in BPCGW.

The Organic Pollutant Characteristics of Lurgi Coal Gasification Wastewater before and after Ozonation

The effluent of distilled and extracted Lurgi coal gasification wastewater has been found to have low biodegradability and high toxicity, which inhibits further biodegradation. However, ozonation enhances the biodegradability and reduces the toxicity of this effluent, enabling further biological treatment and increased removal of organic materials. In this study, the dissolved organic matters in Lurgi coal gasification wastewater were isolated into six classes by resin adsorbents, after which TOC, UV254, UV-Vis, and 3D EEM were employed to quantitatively and qualitatively analyze organic materials in each part of the fractionated samples. The HoA and HiN fraction accounted for large amounts of the Lurgi coal gasification wastewater, and their TOC values were about 380.21 mg·L−1 and 646.84 mg·L−1, respectively. After ozonation, the TOC removal rates of HoA and HiN reached 42.85% and 67.13%, respectively. The UV254 of HoA was basically stable before and after ozonation, while that of HiN increased continuously because a portion of the humic macromolecular organic materials in HoA was oxidized to HiN. Additionally, UV-Vis analysis revealed that the larger molecular organics of HoA were oxidized during ozonation, resulting in high biodegradability. Finally, the 3D EEM spectra indicated that the macromolecular organics were oxidized to smaller molecules with the degradation of soluble microbial by-products.

Inhibitory effect of high phenol concentration in treating coal gasification wastewater in anaerobic biofilter

In this paper, the inhibition of methanogens by phenol in coal gasification wastewater (CGW) was investigated by both anaerobic toxicity tests and a lab-scale anaerobic biofilter reactor (AF). The anaerobic toxicity tests indicated that keeping the phenol concentration in the influent under 280mg/L could maintain the methanogenic activity. In the AF treating CGW, the result showed that adding glucose solution as co-substrate could be beneficial for the quick start-up of the reactor. The effluent chemical oxygen demand (COD) and total phenol reached 1200 and 100mg/L, respectively, and the methane production rate was 175mLCH₄/gCOD/day. However, if the concentration of phenol was increased, the inhibition of anaerobic micro-organisms was irreversible. The threshold of total phenol for AF operation was 200-250mg/L. The extracellular polymeric substances (EPS) and particle size distribution of anaerobic granular sludge in the different stages were also examined, and the results indicated that the influence of toxicity in the system was more serious than its effect on flocculation of EPS. Moreover, the proportion of small size anaerobic granular sludge gradually increased from 10.2% to 34.6%. The results of high through-put sequencing indicated that the abundance of the Chloroflexi and Planctomycetes was inhibited by the toxicity of the CGW, and some shifts in the microbial community were observed at different stages.

Membrane electro-oxidizer: A new hybrid membrane system with electrochemical oxidation for enhanced organics and fouling control

The synergistic combination of membrane filtration with advanced oxidation is of particular interest for next-generation wastewater treatment technologies. A membrane electro-oxidizer (MEO) hybridizing a submerged microfilter and an electrochemical cell was developed and investigated for tertiary treatment of secondary industrial (textile) wastewater effluent. Laboratory- and pilot-scale MEO systems were designed and evaluated for treatment efficiency and membrane fouling control. The MEO achieved substantial removal of color (50-90%), turbidity (>90%), and bacteria (>4 log) as well as chemical oxygen demand (13-31%) and 1,4-dioxane (∼25-53%). Fluorescence-based parallel factor analysis disclosed the degradation of humic-like organics with fluorophores. Size exclusion chromatograms with organic carbon detection confirmed the removal of specific organic molecules with ∼100 Da. While investigating the effects of oxidant quenching agents, reactive chlorine species and hydrogen peroxide were found to be most responsible for the anodic oxidation of secondary effluent organics. The efficacy of membrane fouling mitigation by the MEO was greater when higher electric current densities were applied, but was not dependent on the number of electrochemical cells installed. The MEO is a promising technology for enhanced organics removal with simultaneous fouling control due to its multifunctional active oxidants.

Waste rice straw and coal fly ash composite as a novel sustainable catalytic particle electrode for strengthening oxidation of azo dyes containing wastewater in electro-Fenton process

A novel catalytic particle electrode (CPE) was synthesized from waste rice straw and coal fly ash which was employed to strengthen electro-Fenton treating actual azo dyes containing wastewater. Results showed that the prepared CPE exhibited excellent electro-catalytic activity and significantly improved performance of pollutants removal at near-neutral pH condition, achieving over 73.5 and 90.5% of chemical oxygen demand (COD) and color removal percentages, respectively, allowing discharge criteria to be met. And the electro-Fenton with CPE improved the biodegradability of wastewater in terms of BOD₅/COD, resazurin dehydrogenase activity, and toxicity, indicating the potential application of integrated biosystem for this type of wastewater. On the basis of inhibition of different radical scavengers and fluorescence test, it was deduced that the main contribution of the novel CPE was responsible for catalyzing electro-generate H₂O₂ to produce more hydroxyl radicals in electro-Fenton, and the positive role of generation of superoxide anion at near-neutral pH was also proved, further the possible reaction mechanism was proposed. Moreover, CPE showed the advantages of superior stability and low cost at successive runs and the results offered new insights for sustainable use of waste materials.