Effect of pre-treatments on the production of biofuels from Phaeodactylum tricornutum.

Several characteristics make Phaeodactylum tricornutum potential candidate for biofuels production such as methane and biodiesel. For this reason, some alternatives are evaluated in this manuscript to improve the conversion of this microalgae into methane. One of these alternatives is the addition of sewage sludge to Phaeodactylum tricornutum for anaerobic co-digestion. Although the co-digestion resulted in lack of synergy, the absence of inhibition indicated that both substrates could be co-digested under certain circumstances, for example if microalgae are cultivated for wastewater treatment purposes. The extraction of lipids using organic solvents has been evaluated for biodiesel production but also as a pre-treatment for anaerobic digestion. The results revealed that the type of solvent influences lipid and biodiesel yields. The high polarity of the mixture methanol/hexane increased the lipid and the biodiesel yields from 10 ± 1 to 53 ± 2 gLipids/100 gVS and from 7 ± 1 to 11 ± 1 gBiodiesel/100 gVS compared with hexane. However, none of these solvents affected the composition of biodiesel. Regarding the methane production after the extraction, it yielded 257 ± 8 and 180 ± 6 mLCH4/gVS from lipid-extracted P. tricornutum using hexane and methanol/hexane respectively. The methane production from the raw microalga was 258 ± 5 mLCH4/gVS in the same experiment. The difference in methane production, mainly after the extraction with methanol/hexane, was a consequence of the changes in the composition of the microalgae after extraction. The extraction did not influence the biodegradability. The ultrasonic pre-treatment prior anaerobic digestion completely disrupted the microalgae cells, but the solubilisation of the organic fraction was scarce (<9.5%). The methane production from pre-treated samples was barely 10-11% higher than the obtained from non pre-treated samples, indicating that the refractory nature of the organic fraction in P. tricornutum is the main obstacle for the methane production.

Precise determination of the total nitrogen content in activated sludge by ultrasonic pre-treatment assisted wet method.

The study proposed a method for determining total nitrogen (TN) content in activated sludge by ultrasound pre-treatment assisted wet method. Based on the single-factor experiment, with the TN content as the response value, the response surface methodology was employed to examine the individual and interactive effects of three factors: the dilution multiple of the sludge mixture, ultrasonic time, and ultrasonic power. At the same time, the physico-chemical parameters and the digestion-oxidation parameters were optimised. The results indicated that the optimal parameters were as follows; sludge dilution multiple of 225 times, stirring rate of 400 r/min, ultrasonic time of 22 minutes, ultrasonic power of 720 W, and optimal added volume of potassium persulfate at 8 mL with a digestion time of 40 minutes. The relative standard deviation (RSD) for the parallel determination of TN in sludge samples using ultrasonic pre-treatment assisted wet method was ≤2.77%, with a spike recovery rate of 98.49-101.43%. The method, ultrasonic pre-treatment assisted wet method to determine TN concentration in activated sludge, was simpler to operate, more accurate.

Effects of combined ultrasonic and grinding pre-treatments on anaerobic digestion of vinegar residue: organic solubilization, hydrolysis, and CH4 production.

ABSTRACTThe high lignocellulose content of vinegar residues (VR) limits their biochemical methane potential (BMP) in anaerobic digestion (AD). However, unlike reported high cellulosic materials such as straw and grass, single pre-treatment with ultrasonication or grinding only slightly improved VR AD, due to the high protein and carbohydrate contents of VR. This study used statistical analysis to show that the methane yield, protein and polysaccharide release, and hydrolysis performance during VR AD were significantly enhanced with a combined grinding-ultrasound pre-treatment. Specifically, at 60 min of ultrasonic, the group with the combined pre-treatment (60 min + RS) showed the highest VR BMP (∼307.1 mLCH4/gVS), 68.7% greater than that in the control group. This group also exhibited optimal conditions for dissolution of polysaccharide and protein, with accumulated amounts of ∼500 and 1600 mg/L, respectively. The highest volatile fatty acid (VFA) concentration in the 60 min + RS group was 61.5% higher than that in the control group. Both dissolution and hydrolysis experiments suggested that ultrasound accelerated protein release from VR, particularly after the particle size was reduced, and that the grinding pre-treatment had a positive effect on polysaccharide release.

Comprehensive role of thermal combined ultrasonic pre-treatment in sewage sludge disposal.

Thermal/ultrasonic pre-treatment of sludge has been proven to break the hydrolysis barriers of sewage sludge (SS) and improve the performance of anaerobic digestion (AD). In this study, the objective was to investigate whether the combination of two pre-treatment methods can achieve better results on the AD of SS. The results indicated that, compared with the control group and separate pre-treatment groups, the thermal combined ultrasonic pre-treatment presented more obvious solubilization of soluble proteins, polysaccharides, and other organic matters in SS. The combined method promoted the dissolution of protein-like substances more effectively, with biogas production increased by 19% and the volatile solid (VS) removal rate improved to above 50% compared with the control group. The capillary suction time is reduced by about 85%, which greatly improved the dewatering performance of SS. In addition, the combined method has advantages in degrading sulfonamide antibiotics, roxithromycin and tetracycline. Particularly, by analyzing the interaction between the degradation of different antibiotics and the composition of dissolved organic matters (DOMs), it was found that the composition of DOMs could affect the degradability of different antibiotics. Among them, the high content of tyrosine-like and tryptophan-like was conducive to the degradation of sulfamethoxazole, and the high content of fulvic acid-like and humic acid-like was conducive to the degradation of roxithromycin and tetracycline. This work evaluated the comprehensive effect of thermal combined ultrasonic pre-treatment on SS disposal and provided useful information for its engineering.

Effects of ultrasonic pre-treatment on physicochemical properties of proteins extracted from cold-pressed sesame cake.

Sesame is an oil crop with high nutritional value. Protein is one of the main ingredients of sesame, however research on protein of cold-pressed sesame cake is limited. This study aimed to investigate the effects of ultrasonic pre-treatment (UPT) on physicochemical properties of proteins (yield, solubility, amino acid composition, surface properties, structural and thermal stability) extracted from the cold-pressed sesame cake, after removing lignans by ultrasonic-assisted extraction. By comparison, the extraction yield of protein was significantly (p ＜ 0.05) increased from 22.24% (without UPT) to 25.95% (with UPT), while the purity (54.08% without UPT, 55.43% with UPT), total amount of essential amino acids (22.48% without UPT, 23.10% with UPT) and non-essential amino acids (37.48% without UPT, 36.54% with UPT) were not significantly influenced. Besides, UPT slightly reduced the solubility, foaming capacity and stability (FC and FS) of protein. In addition, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermal stability (TG) analysis demonstrated that UPT could disorder and loose protein molecular structure, resulting in the change of morphology, secondary structure and thermal stability. In conclusion, this study provides a way for the separation and future application of sesame cake protein. UPT is a good option to remove the lignans from sesame cake proteins.

Influence of ultrasound pre-treatment on ilmenite surface chemical properties and collectors' adsorption behaviour.

In this study, we used flotation tests, Fourier transform infrared spectroscopy (FTIR), zeta potential, X-ray photoelectron spectroscopy (XPS), and microcalorimetry measurements to investigate the flotation and possible adsorption mechanisms of the ilmenite surface before and after ultrasonic pre-treatment. Flotation results show that under optimum conditions, the promotion effect of sonication on ilmenite is remarkable. The maximum recovery is 89.54% for ultrasonicated ilmenite at a pH of 4-5. For pH of 8-9, recovery increased again to 66.34%. Microcalorimetry indicates that the adsorption-driven heat release (-Qads) is higher for ultrasonicated ilmenite than for raw one. After pre-treatment, the iso-electric point (IEP) changed from pH 6.2 to pH 4.2. FTIR spectra and zeta potential measurements indicated that metal ions as active sites on the ilmenite surface are probably changed by the ultrasonic treatment. XPS analysis shows that ultrasonic treatment can promotes the oxidation of Fe2+ to Fe3+ and improves the solubilization of Ca2+ and Mg2+ in the pH range of 4-5. Under weakly alkaline condition, ultrasound also can make Ca2+ and Mg2+ re-absorb onto the ilmenite surface as main active sites.

Application of weak ultrasonic treatment on sludge electro-osmosis dewatering.

Ultrasonic treatment is a good method of facilitating sewage sludge dewatering characteristics. It can also promote the potential of sludge electro-osmosis dewatering (EDW), which is an accepted method of deep dewatering, but the treatment method and optimizing conditions should be determined by performing experiments. In this study, we consider two treating methods: ultrasonic pre-treatment, which uses ultrasonic treatment as sludge pre-treatment before electro-osmosis dehydration, and ultrasonic coupling, which uses ultrasonic and electric fields simultaneously. Using sludge from the Tianjin Jizhuangzi sewage treatment plant, we analyze the influence of ultrasonic intensity and treatment time on sludge dewatering by performing two different methods. The results show that they effectively facilitated sludge EDW. Under the same conditions, i.e. 2 cm cake initial thickness, voltage of 60 V for 5 min, and 0.1 MPa mechanical pressure for 5.5 min, the optimum processing conditions for ultrasonic pre-treatment were found to be 0.510 W/cm2 and 3.5 min, the dehydration rate reached 34.71%, and the optimum conditions for ultrasonic coupling were 0.255 W/cm2 and 3.5 min, while the dehydration rate reached 40.78%. The dehydration rates for both approaches were clearly better than 17.40%, which was obtained under pure electro-osmosis dehydration. To compare the effects of ultrasonic pre-treatment and ultrasonic coupling on the electro-osmosis dehydration process, in this paper, we present the curves of dehydration rate, electric current, electro-osmosis flow, and scanning electron microscopy for dewatered sludge. Compared with the ultrasonic pre-treatment method, the effect of ultrasonic coupling on electro-osmosis dehydration was more obvious.

Tube reactors as a novel ultrasonication system for trouble-free treatment of sludges.

The performance of a novel low-maintenance tube reactor for ultrasonic treatment of sludge has been evaluated. The effects of sonication on the release of soluble chemical oxygen demand (sCOD) and anaerobic digestibility of raw and digested sewage sludge as well as agricultural sludge were studied. Results suggest that solubilization and digestibility is dependent on both type of sludge and the energy input. Digested and raw sludge showed high degree of solubilization, however, methane production was only increased for digested sludge. Agricultural sludge was not significantly affected by ultrasonic treatment neither concerning sCOD release nor methane production. The configuration of the ultrasonic system (serial vs. parallel operation) did not show a significant difference in both sCOD release and methane production. However, parallel operation tends to perform better for digested sludge, while serial operation tends to perform better for raw sludge. The strongest effect was observed for the treatment of digested sludge by increasing the methane production by more than 60%, although with a very intensive energy input of more than 5,000kJ per kg total solids. Hence, tube reactors seem to be an attractive alternative to sonotrode-based systems achieving similar performance at low maintenance with great potential especially for digested sludge.

Effects of ultrasound pretreatment on the characteristic evolutions of drinking water treatment sludge and its impact on coagulation property of sludge recycling process.

Large amounts of drinking water treatment sludge (DWTS) are produced during the flocculation or flotation process. The recycling of DWTS is important for reducing and reclaiming the waste residues from drinking water treatment. To improve the coagulation step of the DWTS recycling process, power ultrasound was used as a pretreatment to disintegrate the DWTS and degrade or inactivate the constituents that are difficult to remove by coagulation. The effects of ultrasound pretreatment on the characteristics of DWTS, including the extent of disintegration, variation in DWTS floc characteristics, and DWTS dewaterability, were investigated. The capacity of the recycling process to remove particulates and organic matter from low-turbidity surface water compared to a control treatment process without DWTS was subsequently evaluated. The coagulation mechanism was further investigated by analyzing the formation, breakage, and re-growth of re-coagulated flocs. Our results indicated that under the low energy density applied (0.03-0.033 W/mL) for less than 15 min at a frequency of 160 kHz, the level of organic solubilization was less elevated, which was evidenced by the lower release of proteins and polysaccharides and lower fluorescence intensities of humic- and protein-like substances. The applied ultrasound conditions had an adverse effect on the dewaterability of the DWTS. Ultrasound pretreatment had no significant impact on the pH or surface charge of the DWTS flocs, whereas particle size decreased slightly and the specific surface area was moderately increased. The pollution removal capacity decreased somewhat for the recycled sonicated DWTS treatment, which was primarily ascribed to organic solubilization rather than variability in the floc characteristics of sonicated DWTS. The main coagulation mechanism was floc sweeping and physical adsorption. The breakage process of the flocs formed by the recycling process displayed distinct irreversibility, and the flocs were stronger and more resistant to breakage compared to those from the control treatment.