Thermal Pretreatment Methods Research Articles

Biogas production from pistachio (Pistacia vera L.) processing waste

Abstract Turkey is the third largest producer of pistachio ( Pistacia vera L.) after Iran and United States. Harvested pistachio nuts are covered with organic hull which is removed by de-hulling process. Most of the pistachio by-products which are produced during de-hulling process are considered as agricultural waste and often mixed with soil, to a lesser extent are used as feedstuff by local livestock farmers and a small portion is used as herbal medicine. Due to its high organic and phenolic content as well as high solids concentration, pistachio processing wastes create significant waste management problems unless they are properly managed. However, there is not a well-established waste management method compensating the waste generated during the processing of pistachios. This study investigated the anaerobic treatability and biogas generation potential of pistachio hull waste. The effect of pre-treatment on biogas generation potential was investigated. For this purpose, Biochemical Methane Potential (BMP) Assays were conducted for two Chemical Oxygen Demand (COD) concentrations of 22 and 33 g tCOD l −1 at the absence and presence of chemical and thermal pre-treatment methods. The results revealed anaerobic digestion of the pistachio de-hulling wastes and subsequent biogas production as a renewable energy source are possible. The observed percent COD removal and methane yield values of the pre-treated pistachio de-hulling waste samples were significantly higher than the raw pistachio de-hulling waste. The highest methane yield was observed as 213.4 ml CH 4 /g COD.

Torrefaction of Solid Olive Mill Residue

Solid olive mill residue (SOMR), a lignocellulosic material obtained from olive oil extraction, is a potential attractive source of biomass for energy generation. Although SOMR can be directly combusted, a pretreatment can reduce the oxygen and moisture contents of raw SOMR for efficient energy generation. Torrefaction is a promising thermal pretreatment method for improving fuel characteristics of raw SOMR. In this study, torrefaction characteristics of SOMR were investigated at three different torrefaction temperatures and holding times. Ultimate and proximate analysis results of torrefied SOMR were compared with dried SOMR. Results indicate that an increased torrefaction temperature and holding time can lead to a more qualified solid fuel with higher carbon content, increased higher heating value (HHV), and reduced oxygen content. Further, increased HHV and removal of volatiles are indicators of more energy-dense solid fuel obtained from SOMR. Experimental results revealed that moderately severe torrefaction conditions with holding times not exceeding 30 minutes are suitable for torrefaction of SOMR.

가열 전처리에 따른 피망의 품질 특성 변화

The thermal pre-treatment is an important process to minimize quality change in main cooking or storage. This study was conducted to investigate the effect of different thermal pre-treatment methods (blanching, steaming, and stir-frying) on the quality properties of bell pepper (BP). Washed and sliced BP were treated by blanching (100°C, 1-10 min), steaming (100°C, 1-10 min), and stir-frying with oil (180°C, 10-70 sec). Raw and treated BP was measured for color, pH, hardness, proximate composition, ascorbic acid, free sugar, organic acid, and peroxidase activities. Color and hardness were significantly decreased by blanching, steaming, and stir-frying. Stir-frying, in particular, rapidly decreased the ΔE values and hardness of BP. Blanching and steaming slightly increased the pH compared with raw BP, whereas stir-frying rapidly decreased the pH values. Results showed that the proximate composition, ascorbic content, free sugar content, and organic acid content were significantly (p<0.05) affected by the thermal pre-treatment and that the loss rate varied among individual compounds. Blanching, steaming, and stir-frying significantly reduced the ascorbic acid content (29.4-55.2%), fructose content (8.6-45.1%), and glucose content (8.1- 41.9%) in the BP. Oxalic acid, citric acid, succinic acid, and furmaric acid as organic acid in BP were detected and their contents were significantly (p<0.05) reduced during thermal pre-treatment. In conclusion, the results demonstrated that steam treatment for 3 min could be the best optimal thermal pre-treatment condition for BP to minimize the quality changes.

Enhanced anaerobic digestion of food waste by thermal and ozonation pretreatment methods

Treatment of food waste by anaerobic digestion can lead to an energy production coupled to a reduction of the volume and greenhouse gas emissions from this waste type. According to EU Regulation EC1774/2002, food waste should be pasteurized/sterilized before or after anaerobic digestion. With respect to this regulation and also considering the slow kinetics of the anaerobic digestion process, thermal and chemical pretreatments of food waste prior to mesophilic anaerobic digestion were studied. A series of batch experiments to determine the biomethane potential of untreated as well as pretreated food waste was carried out. All tested conditions of both thermal and ozonation pretreatments resulted in an enhanced biomethane production. The kinetics of the anaerobic digestion process were, however, accelerated by thermal pretreatment at lower temperatures (<120 °C) only. The best result of 647.5 ± 10.6 mlCH4/gVS, which is approximately 52% higher as compared to the specific biomethane production of untreated food waste, was obtained with thermal pretreatment at 80 °C for 1.5 h. On the basis of net energy calculations, the enhanced biomethane production could cover the energy requirement of the thermal pretreatment. In contrast, the enhanced biomethane production with ozonation pretreatment is insufficient to supply the required energy for the ozonator.

Integrated Hydrolyzation and Fermentation of Sugar Beet Pulp to Bioethanol

Sugar beet pulp is an abundant industrial waste material that holds a great potential for bioethanol production owing to its high content of cellulose, hemicelluloses, and pectin. Its structural and chemical robustness limits the yield of fermentable sugars obtained by hydrolyzation and represents the main bottleneck for bioethanol production. Physical (ultrasound and thermal) pretreatment methods were tested and combined with enzymatic hydrolysis by cellulase and pectinase to evaluate the most efficient strategy. The optimized hydrolysis process was combined with a fermentation step using a Saccharomyces cerevisiae strain for ethanol production in a single-tank bioreactor. Optimal sugar beet pulp conversion was achieved at a concentration of 60 g/l (39% of dry weight) and a bioreactor stirrer speed of 960 rpm. The maximum ethanol yield was 0.1 g ethanol/g of dry weight (0.25 g ethanol/g total sugar content), the efficiency of ethanol production was 49%, and the productivity of the bioprocess was 0.29 g/l·h, respectively.

RESEARCH ON THE PROPERTIES OF THERMAL SPRAYED NI-CR-SI-FE-B COATINGS / TERMINIU BŪDU UŽPURKŠTŲ NI-CR-SI-FE-B DANGŲ SAVYBIŲ TYRIMAS

The article deals with the flame sprayed Ni-Cr-Si-Fe-B coating on aluminum alloy substrates. Before the thermal spraying process, aluminum samples were modified applying chemical, mechanical and thermal processing pre-treatment methods. The main aluminum surface treatment was removing an oxide layer from the surface and improving the exploitation properties of nickel-based coatings. The work involved coating microstructure, porosity, adhesion and microhardness tests. The dependence of the estimated exploitation properties of flame spray coatings on aluminum surface preparation methods and technological parameters of spraying has been established. Santrauka Straipsnyje nagrinėjamos liepsniniu būdu ant aliuminio lydinių substratų užpurkštos Ni-Cr-Si-Fe-B dangos. Aliuminio bandiniai prieš terminį purškimą buvo apdoroti cheminiais, mechaniniais ir terminiais būdais. Pagrindinis aliuminio paviršiaus apdorojimo tikslas buvo pašalinti oksidų sluoksnį nuo paviršiaus ir pagerinti nikelio pagrindo dangų eksploatacines savybes. Atlikti dangos mikrostruktūros, porėtumo, adhezijos ir mikrokietumo tyrimai. Nustatyta liepsninio purškimo būdu gautų dangų eksploatacinių savybių priklausomybė nuo aliuminio paviršiaus paruošimo būdų ir purškimo technologinių parametrų.

Influence of proteins content in the feed on the course of membrane distillation

The formation of deposit on the membrane surface (fouling) is one of the major operating problems of membrane processes. The influence of proteins on the course of membrane fouling was investigated during the whey concentration process. The Fourier transform infrared spectroscopy method was applied in order to determine the composition of the deposit precipitated from the feed as well as accumulated on the membrane surface on the feed side. The intensity of fouling can be limited by the pretreatment of feed and the selection of operating parameters of membrane distillation. The thermal and chemical pretreatment methods were used for whey deproteinization. The whey was subsequently concentrated by direct contact membrane distillation using polypropylene membranes at 323, 333, and 343 K. The concentrated whey contained all components of the feed.

Enhancement in mesophilic aerobic digestion of waste activated sludge by chemically assisted thermal pretreatment method

The effects of hybrid microwave (MW)-alkali pretreatment methods on the efficiency of mesophilic aerobic digestion were studied. The MW-alkali pretreatment (95°C-pH 12) was observed to enhance the sludge solubilization synergistically from 0.5% (raw) to 52.5% (MW-NaOH) and 48.7% (MW-KOH), which are 20% greater than the additive value of MW only and alkali only (16%MW+28.4%NaOH=44.4% and 16%MW+25.5KOH=41.5). The higher VSS solubilization was observed for hybrid MW-NaOH (53.9%) and MW-KOH (47.4%) methods. The batch mesophilic (35°C) aerobic digestion system led to 81.1% TCOD degradation and 72.4% VSS degradation at 20days of retention time, with 35% higher TCOD and VSS reduction in comparison with the control system. The filterability of microwave-alkali pretreated sludge was improved remarkably after aerobic digestion. Moreover, the proposed method is capable of effectively sanitize the sewage sludge and produce Class A biosolids.

Improving the sludge disintegration efficiency of sonication by combining with alkalization and thermal pre-treatment methods

One of the most serious problems encountered in biological wastewater treatment processes is the production of waste activated sludge (WAS). Sonication, which is an energy-intensive process, is the most powerful sludge pre-treatment method. Due to lack of information about the combined pre-treatment methods of sonication, the combined pre-treatment methods were investigated and it was aimed to improve the disintegration efficiency of sonication by combining sonication with alkalization and thermal pre-treatment methods in this study. The process performances were evaluated based on the quantities of increases in soluble chemical oxygen demand (COD), protein and carbohydrate. The releases of soluble COD, carbohydrate and protein by the combined methods were higher than those by sonication, alkalization and thermal pre-treatment alone. Degrees of sludge disintegration in various options of sonication were in the following descending order: sono-alkalization > sono-thermal pre-treatment > sonication. Therefore, it was determined that combining sonication with alkalization significantly improved the sludge disintegration and decreased the required energy to reach the same yield by sonication. In addition, effects on sludge settleability and dewaterability and kinetic mathematical modelling of pre-treatment performances of these methods were investigated. It was proven that the proposed model accurately predicted the efficiencies of ultrasonic pre-treatment methods.

Improving anaerobic conversion of pulp mill secondary sludge to biogas by pretreatment

We examined the effectiveness of thermal, caustic, and sonication pretreatment methods in improving anaerobic conversion to biogas of secondary sludge samples obtained from a kraft mill and a sulfite mill. All three methods improved the anaerobic digestion rate and the biogas yield of the sludge samples. Thermal pretreatment was the most effective, followed closely by caustic pretreatment, and sonication the least. The total biogas productions per unit of chemical oxygen demand of sulfite sludge and kraft sludge samples were respectively 1.2 and 3 times higher with pretreatments than without. Also, the biogas production from the untreated sulfite mill sludge was 4 times higher than that from the untreated kraft mill sludge.

Evaluation of carbonization as a thermal pretreatment method for landfilling by column leaching tests

To evaluate carbonization as a thermal pretreatment method for landfilling, the releasing characteristics of organic and inorganic constituents from carbonization residue derived from shredded residue of bulky waste was investigated by means of batch and column leaching tests. Shredded residue of bulky waste itself and its incineration ash were tested together to compare pretreatment methods. In batch leaching tests at a liquid/solid ratio of 10, the release of organic carbon from carbonization residue was at a remarkably low level. Besides, carbonization contributed to immobilize heavy metals such as chromium, cadmium, and lead within its residue. In column tests, the discharges of organic constituents were lowest from carbonization residue under aerobic conditions due to microbial activity. The leaching of Cd, Cr, Pb, and Cu from carbonization residue was suppressed under anaerobic conditions; however, this suppression effect tended to be weaker under aerobic conditions. From the results showing that the total releasing amounts of organic and inorganic constituents from carbonization residue are so low as to be comparable to that of incineration ash, carbonization can be considered as one of the thermal pretreatment methods of organic wastes.

The use of the three point bend test to quantify the effects of thermal pre-treatment on rock strength

A significant problem of thermal pre-treatment methods is that of assessing the influence of these methods on the ore strength. Single practice breakage tests may be used to determine the effect of thermal pre-treatment on intrinsic strength parameters of the material as opposed to bulk parameters. In order to test the validity and sensitivity of a new method, the Three-point bend test, experiments were conducted on a heterogenous carbonatite ore and a homogenous shap granite which were thermally pre-treated. The test successfully detected the sharp strength decrease (up to 87%) due to quartz phase inversion within the granite as well as reductions of up to 80% in the carbonatite due to the thermal pre-treatment. Results correspond well to those of the Berry and Bruce method. Overall the Three point bend test is sensitive enough to detect changes in rock strength whilst being a much simpler method than conventional grinding tests.

Minimizing of foaming in digesters by pre-treatment of the surplus-sludge

Several reasons can lead to the emergence of foam in digesting tanks, for instance overloading or the impact of hydrophobic substances. Furthermore, the foaming is in regular periods going together with the emergence of filamentous microorganisms. Up to now, several strategies to avoid foaming have been tested out (for instance reduction of the sludge load in the activated sludge stage, lowering of the sludge level in the digestion tank, dosage of anti foaming agents), but these have been done relatively unsystematically and with more or less success. For our contribution, laboratory-scale digestion tests were run to analyse mechanical and thermal pre-treatment methods for the destruction of the surplus sludge. Whereas the disintegration by a high pressure homogeniser did only achieve a low reduction of the foam phase, the thermal pre-treatment at 121°C made for an effective subduing of the foam emergence. Both methods allowed for a cutting up of the filaments, but only the heating up effected the reduction of the hydrophobic substances; thus, the foaming is possibly caused by them.

The effect of municipal solid waste pretreatment on landfill behavior: a literature review

Landfilling is one of the most widely used municipal solid waste (MSW) disposal methods worldwide. It is the necessary part of an integrated solid waste system, since all waste treatment processes have residues that cannot be further reused or recovered and are eventually landfilled. Thermal, mechanical and biological pretreatment techniques are used, often in combination, prior to landfilling. The primary aim is the recovery of certain components and energy production. However, pretreatment techniques can also be used with the ultimate objective of controlling landfill behavior, that is the biological and physicochemical processes that take place within a landfill. Two ways a landfill can be managed in the future are: a final storage quality depository, in which environmental emissions are kept to a minimum; or a controlled bioreactor, in which enhanced methane production rates and methane utilization are the goals. Thermal, mechanical and biological pretreatment methods can be combined to achieve either of the above goals. Both financial and environmental issues have to be considered when determining the ways landfills will be managed in the future, as part of an optimized integrated waste management system.