Environmental Technology

Zhu, Liang; Zhou, Jiaheng; Yu, Haitian; Xu, Xiangyang

doi: 10.1080/09593330.2014.998717pmid: 25558911

The hydraulic shear acts as an important selection pressure in aerobic sludge granulation. The effects of the hydraulic shear rate and reactor configuration on structural characteristics of aerobic granule in view of the hydromechanics. The hydraulic shear analysis was proposed to overcome the limitation of using superficial gas velocity (SGV) to express the hydraulic shear stress. Results showed that the stronger hydraulic shear stress with SGV above 2.4 cm s−1 promoted the microbial aggregation, and favoured the structural stability of the granular sludge. According to the hydraulic shear analysis, the total shear rate reached (0.56–2.31)×105 s−1 in the granular reactor with a larger ratio of height to diameter (H/D), and was higher than that in the reactor with smaller H/D, where the sequencing airlift bioreactor with smaller H/D had a high total shear rate under the same SGV. Results demonstrated that the granular reactor could provide a stronger hydraulic shear stress which promotes the formation and structural stability of aerobic granules.

Simsek, Halis; Kobya, Mehmet; Khan, Eakalak; Bezbaruah, Achintya N.

doi: 10.1080/09593330.2014.999829pmid: 25558868

The removal of cyanide (CN−) from aqueous solutions using a strongly basic ion-exchange resin, Purolite A-250, was investigated. The effects of contact time, initial CN− concentration, pH, temperature, resin dosage, agitation speed, and particle size distribution on the removal of CN− were examined. The adsorption equilibrium data fitted the Langmuir isotherm very well. The maximum CN− adsorption capacity of Purolite A-250 was found to be 44 mg CN− g−1 resin. More than 90% CN− adsorption was achieved for most CN− solutions (50, 100, and 200 mg CN− L−1) with a resin dose of 2 g L−1. The equilibrium time was ∼20 min, optimum pH was 10.0–10.5, and optimum agitation speed was 150 rpm. An increase in adsorption of CN− with increasing resin dosage was observed. Adsorption of CN− by the resin was marginally affected (maximum 4% variation) within an environmentally relevant temperature range of 20–50 °C. Fixed-bed column (20.5 mm internal diameters) experiments were performed to investigate the effects of resin bed depth and influent flow rate on breakthrough behaviour. Breakthrough occurred in 5 min for 0.60 cm bed depth while it was 340 min for 5.40 cm bed depth. Adsorption capacity was 25.5 mg CN− g−1 for 5 mL min−1 flow rate and 3.9 mg CN− g−1 for 20 mL min−1 flow rate. The research has established that the resin can be effectively used for CN− removal from aqueous solutions.

Li, Pengzhang; Wang, Shuying; Peng, Yongzhen; Liu, Yue; He, Janzhong

doi: 10.1080/09593330.2014.1002862pmid: 25619120

Nitrous oxide (N2O) is a potent greenhouse gas, which is produced during nitrifying and denitrifying processes. Some factors and mechanisms affecting N2O emission have been reported in previous literature, but wastewater biological nitrification is accompanied by a dynamic process of dissolved oxygen (DO) consumption and pH reduction, it is more meaningful to study the synergistic effects between DO and pH on N2O production. In this study, the synergistic effects between DO and pH on N2O production were investigated with real domestic wastewater. The results showed that high DO levels and a high pH could improve the oxidation ratio of and the production ratio of while effectively reducing the accumulation ratio of N2O. The was a prerequisite for nitrifier denitrification; when was oxidized completely, there would be no N2O production and an even higher concentration of The pH factor is shown to directly affect N2O emission, although free ammonia and free nitrous acid which changed with pH had no correlation with N2O emission. There were two reasons: (1) pH can influence the flow direction of electrons afforded by NH2OH oxidation; at high pH, electrons were mainly used for combining H+ and O2 (O2 + 4H+ + 4e− = 2H2O), the accumulation of cannot be a result of denitrification, and a higher DO can get more electrons to prefer and (2) was the prerequisite for NH2OH oxidation, since NH2OH oxidation process was the way to provide electrons for nitrifier denitrification.

Brito, Luis Miguel; Mourão, Isabel; Coutinho, João; Smith, Stephen R.

doi: 10.1080/09593330.2014.1002863pmid: 25559143

The feasibility of commercial-scale co-composting of waste biomass from the control of invasive Acacia species with pine bark waste from the lumber industry, in a blend ratio of 60:40 (v:v), was investigated and compared with previous research on the composting of Acacia without additional feedstock, to determine the potential process and end-product quality benefits of co-composting with bark. Pile temperatures rose rapidly to >70 °C and were maintained at >60 °C for several months. Acacia and bark biomass contained a large fraction of mineralizable organic matter (OM) equivalent to approximately 600 g kg−1 of initial OM. Bark was more recalcitrant to biodegradation compared with Acacia, which degraded at twice the rate of bark. Therefore, incorporating the bark increased the final amount of compost produced compared with composting Acacia residues without bark. The relatively high C/N ratio of the composting matrix (C/N = 56) and NH3 volatilization explained the limited increases in content, whereas concentrations of conservative nutrient elements (e.g. P, K, Ca, Mg, Fe) increased in proportion to OM mineralization, enriching the compost as a nutrient source for horticultural use. Nitrogen concentrations also increased to a small extent, but were much more dynamic and losses, probably associated with N volatilization mechanisms, were difficult to actively control. The physicochemical characteristics of the stabilized end-product, such as pH, electrical conductivity and OM content, were improved with the addition of bark to Acacia biomass, and the final compost characteristics were suitable for use for soil improvement and also as horticultural substrate components.

Jiang, Zhou; Yang, Tingting; Zhang, Yanjun; Wang, Jian

doi: 10.1080/09593330.2014.1002864pmid: 25559050

A photosensitizer tetra-α-(2,4-di-tert-butylphenoxy)-phthalocyaninato zinc [ZnPc(OAr)4] was successfully encapsulated in SiO2 nanoparticle by the microemulsion method. The photosensitized composite nanoparticle was able to degrade 2,4,6-trichlorophenol (TCP) in aqueous solution. Under visible light irradiation, the nanoparticles efficiently generated reactive oxygen species; 95.4% of TCP was degraded after 270 min of reaction. Some aromatic compounds and aliphatic carboxylic acids were detected by mass spectrometry as the reaction intermediates. The results were different from those of previously reported photocatalytic reactions, in which valence band holes or hydroxyl radicals functioned as the main oxidants. The photosensitizing composite nanoparticle is potentially applicable to the oxidation of phenol.

Dede, Omer H.; Ozdemir, Saim

doi: 10.1080/09593330.2014.1003251pmid: 25558959

Composts produced from composting municipal sewage sludge with bulking agent, namely hazelnut husk (HH), pine litter (PL), corn straw (CS) and sawdust (SW), were seeded with turfgrass mix and cultivated in a container to compare the suitability of composted substrates to produce turfgrass in greenhouse conditions. The performance of substrate was determined by both substrate properties compared to standard peat and by measuring plant growth parameters on each substrate during turfgrass sod establishment. In general, the physico-chemical properties of all substrates were satisfactory for container substrates, but HH and PL substrates performed better in plant growth parameters than in SW and CS composts. The comprehensive growth index values obtained for plants growing in peat, HH and PL were 0.94, 0.87 and 0.84, respectively, which were higher than those in the CS and SW. Plant growth showed linear above-ground dry matter accumulation in all substrates, but was slower in SW and CS. HH and PL substrates appeared to be suitable for containerized sod production for natural soil and peat substitution. Biosolid proved to be an efficient component as a nutrient source ingredient of composted substrates for turfgrass.

Naz, Iffat; Seher, Shama; Perveen, Irum; Saroj, Devendra P.; Ahmed, Safia

doi: 10.1080/09593330.2014.1003614pmid: 25609155

This research work evaluated the biofilm succession on stone media and compared the biochemical changes of sludge in attached and suspended biological reactors operated under aerobic and anaerobic conditions. Stones incubated (30 ± 2°C) with activated sludge showed a constant increase in biofilm weight up to the fifth and seventh week time under anaerobic and aerobic conditions, respectively, where after reduction (>80%) the most probable number index of pathogen indicators on ninth week was recorded. Reduction in parameters such as biological oxygen demand (BOD) (47.7%), chemical oxygen demand (COD, 41%), nitrites (60.2%), nitrates (105.5%) and phosphates (58.9%) and increase in dissolved oxygen (176.5%) of sludge were higher in aerobic attached growth reactors as compared with other settings. While, considerable reductions in these values were also observed (BOD, 53.8%; COD, 2.8%; nitrites, 28.6%; nitrates, 31.7%; phosphates, 41.4%) in the suspended growth system under anaerobic conditions. However, higher sulphate removal was observed in suspended (40.9% and 54.9%) as compared with biofilm reactors (28.2% and 29.3%). Six weeks biofilm on the stone media showed maximum physiological activities; thus, the operational conditions should be controlled to keep the biofilm structure similar to six-week-old biofilm, and can be used in fixed biofilm reactors for wastewater treatment.

Li, O.L.; Guo, Y.; Chang, J.S.; Saito, N.

doi: 10.1080/09593330.2014.1003981pmid: 25566678

The disposal of enormous amount of stormwater sediments becomes an emerging worldwide problem. Stormwater sediments are contaminated by heavy metals, phosphorus, trace organic and hydrocarbons, and cannot be disposed without treatment. Thermal plasma decontamination technology offers a high decomposition rate in a wide range of toxic organic compound and immobilization of heavy metal. In this study, we compared the treatment results between two different modes of thermal plasma: (1) a non-transferred direct current (DC) mode and (2) a partial DC-transferred mode. The reductions of total organic carbon (TOC) were, respectively, 25% and 80% for non-transferred and partially transferred plasma, respectively. Most of the toxic organic compounds were converted majorly to CxHy. In the gaseous emission, the accumulated CxHy, CO, NO and H2S were significantly higher in partially transferred mode than in non-transferred mode. The solid analysis demonstrated that the concentrations of Ca and Fe were enriched by 500% and 40%, respectively. New chemical compositions such as KAlSi3O8, Fe3O4, NaCl and CaSO4 were formed after treatment in partially DC-transferred mode. The power inputs were 1 and 10 kW, respectively, for non-transferred DC mode and a partially DC-transferred mode. With a lower energy input, non-transferred plasma treatment can be used for decontamination of sediments with low TOC and metal concentration. Meanwhile, partially transferred thermal plasma with higher energy input is suitable for treating sediments with high TOC percentage and volatile metal concentration. The organic compounds are converted into valuable gaseous products which can be recycled as an energy source.

Mampaey, Kris E.; van Dongen, Udo G.J.M.; van Loosdrecht, Mark C.M.; Volcke, Eveline I.P.

doi: 10.1080/09593330.2015.1005029pmid: 25573615

Nitrous oxide emissions from wastewater treatment plants are currently measured by online gas phase analysis or grab sampling from the liquid phase. In this study, a novel method is presented to monitor the liquid phase N2O concentration for aerated as well as non-aerated conditions/reactors, following variations both in time and in space. The monitoring method consists of a gas stripping device, of which the measurement principle is based on a continuous flow of reactor liquid through a stripping flask and subsequent analysis of the N2O concentration in the stripped gas phase. The method was theoretically and experimentally evaluated for its fit for use in the wastewater treatment context. Besides, the influence of design and operating variables on the performance of the gas stripping device was addressed. This method can easily be integrated with online off-gas measurements and allows to better investigate the origin of the gas emissions from the treatment plant. Liquid phase measurements of N2O are of use in mitigation of these emissions. The method can also be applied to measure other dissolved gasses, such as methane, being another important greenhouse gas.

Bilgin, Melayib; Tulun, Şevket

doi: 10.1080/09593330.2015.1006262pmid: 25571768

Biodrying is a variation of aerobic decomposition used for the mechanical–biological treatment organic substances to dry and partially stabilize residual municipal waste. This study focuses on the volume and weight reduction biodegradation of the biodrying process using municipal solid waste and the appearance of a stable, final product. The materials were placed in a reactor with invariant airflow rates of 50 L/h and initial moisture contents of 48.49–50.00%. The laboratory-scale experiments were implemented using a 36-L biodrying reactor equipped with an air supply system, a biomass temperature sensor and air sensors. To determine the effect of temperature on biodrying, the process was repeated at various temperatures between 30 °C and 50 °C. The results obtained indicated that after 13 days, biodrying reduced the volume content of waste by 32% and the final product had a high calorific value (4680 kcal/kg).