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The main aim of the study was to evaluate utilization options of dehydrated waste water sludge (WWS) as fuel and fertilizer. Changes in quality of the final product of three WWS treatment methods were compared - drying, pasteurization and incineration. This paper analyses potential risks and benefits of using waste water sludge as fertilizer and the suitability of using dehydrated and incinerated material as fertilizer. Technological and energy consumption aspects of all three options were analysed. The barriers for implementation of these technologies into common practice are more political than technical. For waste water sludge containing a low content of heavy metals, drying or incineration are more sustainable aftertreatment methods. [ABSTRACT FROM AUTHOR]

Utilization of the sewage sludge is pressing and crucial environmental and economic challenge. High moisture content of the sludge is one of the main difficulties during the process of the sewage sludge utilization. Experimental drying module has been designed and manufactered to identify and verify effectiveness of the main parameters of the thermal drying of the sewage sludge with application of the pneumatic pulse method. The pulser is supposed to be part of the technological scheme in order to speed up the process of drying and saving energy. The pulser supplies hot air into the drying chamber with time intervals by pulse. In the drying chamber the airlow dislodges water molecules from the material by means of pulses and then they are taken away from the drying chamber. For the convenience of the comparison and evaluation of the executed experiment the following general characteristics were selected: drying rate -- i -- kg min-1; power consumption -- q -- kWh kg-1. The greatest effect in application of the pneumatic pulse method for dehydration of the sewage sludge was achieved at the angle of incidence equal to nearly 90° of the airlow on the dried sample and higher temperature. The experiment showed that application of the pneumatic pulse method for dehydration of the sewage sludge allows to reduce power consumption and speed up the process of drying. The process of drying can be executed at lower temperatures. [ABSTRACT FROM AUTHOR]

Sewage sludge is a specific bulky waste and its utilization is hampered by the presence of the environmentally dangerous contaminated substances in the composition presented mainly by heavy metals, pathogens and coagulants. At the same time sewage sludge may serve as a valuable biological raw material. Utilization of the sewage sludge is crucial environmental and economic challenge. Application of the pneumatic pulse method in the technology of dehydration and utilization of the sewage sludge may allow us to speed up the process of drying, reduce power consumption and capital investment, execute process of dehydration at lower temperatures and in less hazardous explosive conditions. Proposed solution is founded on the use of the compact equipment for dehydration and utilization, including pneumatic pulse drying method. For this purpose the pulser--an airflow feeder with required time intervals or pulses, was included in the technological process. In the process of the drying sewage sludge with the use of pneumatic pulse, there is no need to spend all the energy on evaporation of the water molecules and this fact significantly reduces power consumption. Preliminary calculations, taking into account laboratory data, showed that proposed technology of drying sewage sludge allows to reduce power consumption by 25% upon receipt of the dry sludge. The aim of the study is development of sewage sludge dehydration technology for further utilization of design solutions using the pulse method. [ABSTRACT FROM AUTHOR]

The first published studies on stump extraction for bioenergy in Latvia are dated with second half of the 19th century. In the 3rd decade of the 20th century, stump extraction was identified as one of the most prospective and challenging tasks of forest sector to secure sustainable deliveries of solid biofuel. In that time, stump extraction using explosives was considered to be a conventional forestry technology. Now we are returning to the same challenges; however, mechanical power is used instead of explosives to pull and to crash stumps. MCR-500 is the first prototype of combined stump extraction and mounding head for a caterpillar excavator produced in Latvia by joining forces of the LSFRI Silava and engineering company Orvi SIA. The device is supposed to be used for extraction of stumps with a diameter up to 50 cm in coniferous and deciduous tree stands. Additional benefit of the device is ability to prepare soil by making mounds for the following forest regeneration. The article summarizes results of productivity trials of stump extraction and preparation of soil using the MCR- 500 head. In total, 3.5 ha were extracted during the studies. The harvested amount of stumps was estimated using biomass equations; therefore, it might be corrected in further forwarding and comminution studies when an actual amount of biomass is estimated. Average stock of extractable biomass (stumps and coarse roots) in the experimental sites was 28 tons ha-1. Productivity of stump extraction was 2.4...3.4 tons per efficient hour (2.5 tons in case of optimal rate of scarification of soil). Consumption of efficient time for scarification of soil is 3.4...4.3 hours per ha. Figures of productivity of stump extraction are comparable with the ones obtained with similar stump extraction heads. Scarification of soil with stump lifting head consumes twice more time than conventional trenching; however, in wet sites, productivity figures become closer making the excavator competitive. [ABSTRACT FROM AUTHOR]

The most efficient way to dewater sewage sludge is the thermal drying, which simultaneously with the granulation allows obtaining the product in the form of granules, being a non-putrescible fertilizer that is also easy for transportation, storage and bringing into soil. When large volumes of sewage sludge are formed, which are unfit for use in agriculture, application of other utilization methods, such as burning, would be purposeful. The aim is to determine the optimum drying modes of sewage sludge with application of pneumatic pulse method at treatment facilities in the pilot project. To do this, it is necessary to develop a proposal for the design of operating model. The design and making of working model is necessary to determine the optimal conditions for sewage sludge drying at sewage disposal works. The drying process is provided to be realized in a closed-loop cycle (without emission into atmosphere). Due to inner recirculation of dry air, the installation heat consumption is reduced. Calculations have shown that there is economic expediency of using the pneumatic pulse method in sewage sludge thermal drying technology and possibility of using sewage sludge as an alternative fuel. Optimization of sewage sludge thermal drying process with the use of pneumatic pulse method will considerably extend the perspectives for utilization and further use of sewage sludge. [ABSTRACT FROM AUTHOR]

A prototype of a mower-chipper typeharvester was developed for cutting small stems in cooperation between LSFRI Silava and SIA Laflora. The prototype produces chips and eco-pellets of various lengths in short rotation coppice, shelter belts and overgrown agricultural lands. The innovative element of the harvester is use of gravity force (bending of stems by a tractor own weight and formation of bunch of shoots with header and underframe) to feed in circular saws and chipper, thus significantly reducing energy demand for bending of shoots into the chipper, which is the most energy demanding operation in other commercial willow harvesters. Time studies were implemented in Skrīveri region in August 2022 in short rotation coppice fields established in 2011. Willows of tree different ages (1, 3 and 5 years) were harvested. The main factor influencing productivity in the study sites was growing stock of the coppice crops. The driving speed of the base machine cannot be significantly increased to avoid clogging of the chipper infeed and to retain good quality of chips; therefore, reduction of growing stock cannot be compensated with faster driving in the field. It was also noted that wood chip quality becomes significantly worse if the stump diameter of an average shoot is less than 1 cm and the saw blades are more often blocked by thin, flexible shoots. Similarly, clogging related issues were found in the 5 year old plantation. Optimal work conditions were in the 3 year old coppice crop; however, the driving speed of the base machine (MTZ82 tractor) was still too high. The recommended speed in such conditions is 0.8-1.2 km·h-1. The yield obtained in the tests under these conditions in the 3 year old coppice crop was 2.4 tons of dry matter per hour. The productivity could be raised by increasing the power of the base machine. There is still space for technical improvements to avoid clogging of material in the chipper and jamming of saw blades, as well as to improve the quality of chips. [ABSTRACT FROM AUTHOR]

Waste water sewage sludge is one of municipal waste materials that could be used for nutrient recycling in agriculture, plantation forestry or re-cultivated areas. Sewage sludge contains at least 80 % of water and nutrient rich organic materials what could be used for fertilization of bare soils or for energy production instead of landing on landfills. The de-watering process of sludge by using the impulse method has less energy consumption and higher content of dry matter in the final product is reached in comparison with traditional drying. The aim of the study is to elaborate a method for sewage sludge drying, which allows saving the biological value of final organic material. Impulse interval, frequency, air pressure and temperature in the camera are the key factors for an economically effective process and reaching of qualitative final product. The product could be used for fertilization of non-food products, tree planting, perennial grasses for seed production etc. If sludge contains too high concentration of heavy metals, it could be burned for energy production, and just ashes deponent on landfills. The technological and energy consumption aspects of the methods were analyzed. For sewage sludge containing a low content of heavy metals. Drying is more sustainable after - and pretreatment methods before recycling of plant nutrient elements included in sludge organic material for farming. Transport of dried material is more economical as fresh mass, as well dry material does not smell. The barriers for implementation of these technologies into common practice are more political than technical. [ABSTRACT FROM AUTHOR]