Functionality of surfactants in waste-activated sludge treatment: A review

The effects of surfactants (sodium dodecyl sulfate, triton X-100 and cetyl trimethyl ammonium bromide) on the dewaterability of microalgae biomass using pressure filtration

The application of pressure filtration in microalgae harvesting requires chemical pretreatment in order to reduce membrane fouling and to increase water flux. Surfactants have shown potential to enhance microalgae dewaterability by charge neutralization, bridging and releasing extracellular polymeric substances (EPS) and bound water. In this study, the effect of three surfactants including anionic sodium dodecyl sulfate (SDS), non-ionic triton X-100 and cationic cetyl trimethyl ammonium bromide (CTAB) on the dewaterability of Chlamydomonas sp. was investigated. Filtration fluxes and biomass concentrations were used to evaluate the microalgae dewaterability. Based on the results, SDS and Triton X-100 had a negative effect on the dewaterability of microalgae biomass. However, CTAB improved the dewaterability by decreasing the reversible and irreversible fouling resistance. The optimum dosage of CTAB was found to be 1500 mg/L, and resulted in 95.8% and 140% improvement on average water flux and biomass recovery efficiency, respectively.

Study connective capabilities of solid residues from the waste incineration

Currently there is increasingly closer interaction between the importance of environmental protection and efficient promoting of scientific and technological progress in the field of waste incineration. Waste is not only undesirable source of pollution, but if it is effectively used it also has great economic importance. In the Czech Republic 34.5 million tonnes of all wastes was produced in 2017, of which 5.7 million tonnes of municipal waste. 50% of the produced municipal waste was used, 38% of which was used for the material and 12% for energy utilization. 45% of municipal waste was deposited in the landfills. The method of waste incineration is among the major tools to reduce the landfill waste. The use or processing of the product which the process of incineration of municipal and hazardous waste generated can be considered as an obstacle to the favorable reception of this process. Apart from flammable components, waste also contains certain amount of dangerous particles. This is especially the sulfur chlorides, fluorine, PCBs and other heavy decomposable organic substances and heavy metals. This fact puts high demands on the gas cleaning processes followed by neutralization of other products that the incinerator leaves, in which these substances can be contained in higher concentrations than in the original waste. For this reason subsequent stabilization of these toxic substances is necessary to ensure new environmental burdens are avoided when not used properly. The major part of the waste combustion process is made up of ash and slag. One of the most common ways of dealing with these solid residues is disposing them to avoid creating new hazardous waste landfills. Other filtering waste also passes hazardous waste stabilization process before landfilling. Currently there is intensive search for new possibilities for utilization of solid residues from incineration. Nowadays there is emphasis on process control of their pretreatment for the production of draft procedure with its management. Appropriate procedures may minimize the instances of improper use.

A magnetic activated sludge for Cu(ii) and Cd(ii) removal: adsorption performance and mechanism studies

In the present study, a novel magnetic activated sludge (MAS) was successfully synthesized and applied for heavy metal removal.

Impact of dosing order of the coagulant and flocculant on sludge dewatering performance during the conditioning process

The combined use of coagulant and flocculant can achieve excellent dewatering performance. In this study, we investigated the impact of dosing order of the coagulant and flocculant on sludge dewatering performance. The results showed that capillary suction time (CST) values during the coagulation-flocculation process decreased 20-25% compared to those during the flocculation-coagulation process using the same doses of additives. Moisture content of the sludge during the coagulation-flocculation process was lower. The dosing order of coagulants and flocculants during the conditioning process was clearly important for sludge dewatering, and the coagulant should be dosed before the flocculant. Furthermore, a mechanism for the different dewatering performance was proposed: larger agglomerated and destabilized colloid particles formed, and more bound water was released into the sludge bulk solution during the coagulation-flocculation process, compared with the flocculation-coagulation process, which resulted in better dewatering performance, as reflected in the CST value and moisture content of the sludge cake. These results enable a better understanding of combined conditioning with coagulants and flocculants on sludge dewatering.

Coagulation/flocculation in dewatering of sludge: A review

Sludge disposal is an integral part of wastewater treatment systems, and its cost usually accounts for more than half of the total operation cost. Sludge disposal technology is facing challenges and opportunities simultaneously and can still be improved. Sludge dewatering is an essential process in sludge disposal, and it is important for the effective reduction of the final processing cost. Coagulation/flocculation is a relatively mature, cost-effective, user-friendly sludge dewatering technology. In this work, coagulation/flocculation and their combinations with other pretreatments, including dewatering mechanisms, are reviewed. Various coagulants/flocculants used in sludge dewatering, including inorganic coagulants, organic synthetic and natural polymeric flocculants, and bioflocculants, are introduced in detail because coagulants/flocculants are the key in coagulation/flocculation. The different factors that influence the dewatering performance of these coagulants/flocculants are also presented briefly. Moreover, aiming at the complicated composition of sludge and its treatment difficulty, the prospects and technical developments of coagulation/flocculation in sludge dewatering are discussed.

Oriented acidification of wasted activated sludge (WAS) focused on odd-carbon volatile fatty acid (VFA): Regulation strategy and microbial community dynamics

As the main intermediate metabolite in anaerobic digestion of wasted activated sludge (WAS), volatile fatty acids (VFAs) are proper substrate for mixed culture (MC) polyhydroxyalkanoate (PHA) synthesis. To further optimize the performance of MC PHA production process, VFA_{_odd} (i.e., VFA with odd carbon atoms) oriented acidification process was proposed and conducted in this study. Three regulation factors including reaction pH, fraction of added β-cyclodextrin (β-CD) and glycerol were selected and response surface methodology (RSM) was used to enhance and effectively regulate the VFA_{_odd} production while maintaining enough acidification degree in the WAS acidification. High percentage of VFA_{_odd} (larger than 60% and dominated by propionic acid) can be obtained in the operating condition area with glycerol addition ratio (quantified by C/N) ranging from 15 to 20 and reaction pH ranging from 8.0 to 9.5 when β-CD addition was held at zero level (0.2 g/gTSS) according to the RSM. Semi-continuous acidification and MC PHA production assays further verified the reliability and effectiveness of the VFA_{_odd} oriented acidification strategy. Microbial function group related to propionic acid production (G_prop) was defined based on the relationships between system function and microbial community structure, and 13 frequent species were found being involved in the G_prop. Roles of the group members in the oriented acidification were analyzed to understand the mechanisms of the regulation of VFA_{_odd} production at microbial ecological level. A synergistic effect of WAS and glycerol on the VFA_{_odd} production in the acidification process was revealed based on the ecological analysis.

The relationship between volatile fatty acids accumulation and microbial community succession triggered by excess sludge alkaline fermentation

The volatile fatty acids (VFAs) accumulation pattern and microbial community succession were studied during excess sludge (ES) alkaline fermentation at pH of 10.0 with expanded granular sludge blanket reactor over 5 cyclers. Microbial community shifted conspicuously as ES suffered alkaline fermentation. Both VFAs and acid-producing bacteria increased rapidly during the first 8 days fermentation time, and they showed a quite positive correlation relationship. In addition, soluble chemical oxygen demand (SCOD) also dramatically increased during the first 8 days, which implied 8 day was the optimum sludge retention time (SRT) for ES alkaline fermentation and VFAs accumulation time. Illumina Miseq Sequencing analysis indicated that Clostridium, Bacillus, Amphibacillus and Peptostreptococcaceae were the dominant bacteria genus to produce VFAs. Acetic acid took about 84% in total VFAs because among the total acid-producing bacteria most bacteria could produce acetic acid.

Experimental and theoretical analyses on the impacts of ionic surfactants on sludge properties

A large amount of excess waste activated sludge is produced in municipal wastewater treatment plants and should be further disposed to avoid environmental pollution. Ionic surfactants are being widely used for sludge conditioning, but how and to what extent ionic surfactants change the sludge properties remain unclear. In this work, the impacts of two typical ionic surfactants on the flocculability and stability of sludge were investigated by using experimental and theoretical analyses. The treatment of anionic sodium dodecyl sulfate (SDS) resulted in more detachment of extracellular materials and fluorophores from sludge compared to the treatment of cationic trimethyl ammonium bromide (DTAB). Fourier transform infrared spectra analysis indicates the promoted release of proteins and polysaccharides induced by the surfactants. Deteriorated flocculability of sludge was observed for the SDS-treated sludge, while treatment of DTAB slightly affected the overall sludge flocculability. The sludge floc structure became less stable after treatments of both surfactants, as confirmed by the elevated dispersed mass concentration of small particles in shearing tests. The relationship between the content of extracellular polymeric substances, surfactant dose and sludge properties were evaluated and the roles of released extracellular polymeric substances and surfactant dose in affecting sludge flocculability were examined. Extended DLVO approach was adopted to explore the stability of sludge. By using such an integrated approach, the impacts of ionic surfactants on sludge flocculability and stability were revealed, which is useful in understanding the mechanisms of sludge conditioning by surfactant treatment.

Effective treatment of oily scum via catalytic wet persulfate oxidation process activated by Fe2

Oily scum, a hazardous by-product of petroleum industry, need to be deposed urgently to reduce environmental risks. This paper introduces catalytic wet persulfate oxidation (CWPO) process in the treatment of oily scum to realize risk relief. Under the activation of heat and Fe²⁺, persulfate (PS) was decomposed into sulfate radicals and hydroxyl radicals, which played a major role on the degradation of petroleum hydrocarbons. The effects of wet air oxidation (WAO) and CWPO process on the degradation of oily scum were compared. In CWPO process, the total petroleum hydrocarbons (TPHs) content of oily scum was decreased from 92.63% to 16.75%, which was still up to 70.19% in WAO process. The degradation rate of TPHs in CWPO process was about 3.38 times higher than that in WAO process. The great performance of CWPO process was also confirmed by elemental analysis, which indicated that the C and H contents of oily scum were reduced significantly by CWPO process. These results indicated that CWPO process has high potential on the degradation of oily scum for environmental protection.

Implication of graphene oxide in Cd-contaminated soil: A case study of bacterial communities

The application of graphene oxide (GO) has attracted increasing concerns in the past decade regarding its environmental impacts, except for the impact of GO on a metal-contaminated soil system, due to its special properties. In the present work, the effects of GO on the migration and transformation of heavy metals and soil bacterial communities in Cd-contaminant soil were systematically evaluated. Soil samples were exposed to different doses of GO (0, 1, and 2 g kg^-1) over 60 days. The Community Bureau of Reference (BCR) sequential extraction procedure was used to reflect the interaction between GO and Cd. Several microbial parameters, including enzyme activities and bacterial community structure, were measured to determine the impacts of GO on polluted soil microbial communities. It was shown that Cd was immobilized by GO throughout the entire exposure period. Interestingly, the structure of the bacterial community changed. The relative abundance of the major bacterial phyla (e.g., Acidobacteria and Actinobacteria) increased, which was possibly attributed to the reduced toxicity of Cd in the presence of GO. However, GO exerted an adverse influence on the relative abundance of some phyla (e.g., WD272 and TM6). The diversity of bacterial communities was slightly restricted. The functional bacteria related to carbon and the nitrogen cycling were also affected, which, consequently, may influence the nutrient cycling in soil.