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The purpose of this study is to suggest a new formulation for active vibration control of a rectangular plate based on the optimal positions/orientations of piezoelectric actuators/sensors attached to the plate. The free vibration and modal properties are derived by using Rayleigh-Ritz and the transient response by assumed modes methods based on the classical plate theory. Three criteria are proposed for optimal location of piezoelectric patches attached to the simply supported plate. In other words, the optimal positions/orientations of piezoelectric patches can be determined based on spatial controllability/observability gramians of the structure, as well as the consideration of residual modes to reduce the spillover effect. These criteria are used to achieve the optimal fitness function defined for a genetic algorithm optimizer to find the optimal locations/orientations of piezoelectric sensors/actuators. To control the vibrations of the plate, a negative velocity feedback control algorithm is designed. The results of simulations indicate that by locating piezoelectric patches in the optimal positions, the depreciation rate of the structure increases and the amplitudes of the plate vibrations reduce effectively. The effect of number of piezoelectric devices on the active damping property of the system is also analyzed.

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Abstract. In compliance with the requirements of the EU climate and energy package (3 x 20 %), the biomass consumption in energetic industry is systematically growing. As a consequence, a large amount of ashes is produced which requires the management in line with law and ecology. Stringent requirements concerning the chemical composition of ashes prevent the biomass ash from being used in building construction. Specific physicochemical properties of ashes allow for their application in sewage sludge treatment. This paper presents the results of conditioning using ashes from willow combustion in sewage sludge dewatering. The findings could provide a new approach on sewage sludge and biomass ashes utilization.

Możliwość kondycjonowania i odwadniania osadów ściekowych z zastosowaniem popiołów ze spalania biomasyThe wastewater treatment produces a huge amount of excess sludge which has to be removed in line with ecological and legal requirements. Raw sewage sludge is characterized by the high moisture content, over 90 % and the microbiological activity. The high content of water in sewage sludge results in its big volume and generates significant problems with transport and further utilization. As the high moisture content in raw sewage sludge generates significant costs in treatment plants, it is essential to provide effective dewatering. In order to improve the sewage sludge dewatering, conditioning by means of different materials is applied. Chemical conditioning with the application of organic polymers is used in treatment plants more often than any other methods. The drawback of the aforementioned process is the high cost of chemical reagents and for this reason, it is necessary to find inexpensive and effective conditioners. The aim of this paper is the possibility of sewage sludge dewatering after conditioning with the use of biomass ash derived from the biomassfired power plant. The effectiveness of the aforementioned process was based on the capillary suction time (CST) measurement. After conditioning with the use of biomass ash, the article goes on to describe dewater-ability of sewage sludge by vacuum filtration. The results showed that the sewage sludge moisture content decreased as a dosage of biomass ash increased. Mechanical conditioning with the use of biomass ash influenced the increase of filtrate volume after dewatering. Additionally, the application of biomass ash in sewage sludge management confers the earthen structure of sludge which is suitable to the transport and application in the environment. The mixture of ash and sewage sludge might be used as a valuable fertilizer in perennial plants plantations. Owing to agricultural utilization of sewage sludge, fertilizing properties of sludge are used without a minimal risk to human health.

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