Biochemical Oxygen Demand (BOD) is an important factor used to measure water pollution. This article reviews recent developments of microbial biosensors with respect to their applications for low BOD estimation. Four main methods to measure BOD using a biosensor are described: microbial fuel cells, optical methods, oxygen electrode based methods and mediator-based methods. Each of them is based on different principles, thus a different approach is required to improve the limit of detection. A proper choice of microorganisms used in the biosensor construction and/or sample pre-treatment processes is also essential to improve the BOD lower detection limit.

Industry 4.0 will affect the complexity of supply chain networks. It will be necessary to

adapt more and more to the customer and respond within a time interval that is willing

to accept the product waiting. From these considerations, there is a need for a different way

of managing the supply chain. The traditional concept of supply chain as a linear system,

which allows optimizing individual subsystems, thus obtaining an optimized supply chain, is

not enough. The article deals with the issue of supply chain management reflecting demand

behaviour using the methodology Demand Driven MRP system. The aim of the publication

is to extend the knowledge base in the area of demand-driven supply logistics in the

In literature as well as in the university debate, we can observe the increase of interest regarding converting agricultural residues into energy. Furthermore, the energy and climate policies have encouraged the development of biogas plants for energy production. One of the most significant reasons of this escalation is that this technology may be both convenient and beneficial. The produced biogas is not only supposed to cover the energy demand like heat and electricity, the resulting digestate has the prospect of a beneficial fertilizer and can thereby influence the energy management plans. This technology is widely introduced to countries, which have large income from agriculture. Not only does this reduce the use of industrial fertilizers, but also finds use for agricultural residues. One of the countries of this type is Vietnam, which is the fifth largest exporter of rice in the world. Over 55% of greenhouse gas emission in Vietnam comes from agriculture. Using innovative technologies such as biogas, may decrease this value in near future. It may also contribute to more sustainable agriculture by decreasing traditional fields burning after the harvesting period. The goal of this research paper is to estimate the possible production of biogas from rice straw to cover the energy demand of the rice mill. Four possible scenarios have been considered in this paper, the present situation and where electricity, energy or both were covered by biogas from agricultural residues. An attempt was made to answer the question whether the amount of biogas produced from agricultural residues is enough for both: electricity and energy supply, for the rice mill. If not, how much rice straw must be delivered from other sources, from which rice is not delivered to the rice mill. The base of the assumptions during the estimation of various values were statistics from FAO and other organizations, secondary sources and data from the existing rice mill in Hậu Mỹ Bắc B in Mekong delta in Vietnam.

In this article, we review the research state of the bullwhip effect in supply chains with

stochastic lead times. We analyze problems arising in a supply chain when lead times are

not deterministic. Using real data from a supply chain, we confirm that lead times are

stochastic and can be modeled by a sequence of independent identically distributed random

variables. This underlines the need to further study supply chains with stochastic lead times

and model the behavior of such chains.

In this paper, the results of correlations between air temperature and electricity demand by linear regression and Wavelet Coherence (WTC) approach for three different European countries are presented. The results show a very close relationship between air temperature and electricity demand for the selected power systems, however, the WTC approach presents interesting dynamics of correlations between air temperature and electricity demand at different time-frequency space and provide useful information for a more complete understanding of the related consumption.

Results of the studies for determining fractions of organic contaminants in a pretreated petrochemical wastewater flowing into a pilot Aerated Submerged Fixed-Bed Biofilm Reactor (ASFBBR) are presented and discussed. The method of chemical oxygen demand (COD) fractionation consisted of physical tests and biological assays. It was found that the main part of the total COD in the petrochemical, pretreated wastewater was soluble organic substance with average value of 57.6%. The fractions of particulate and colloidal organic matter were found to be 31.8% and 10.6%, respectively. About 40% of COD in the influent was determined as readily biodegradable COD. The inert fraction of the soluble organic matter in the petrochemical wastewater constituted about 60% of the influent colloidal and soluble COD. Determination of degree of hydrolysis (DH) of the colloidal fraction of COD was also included in the paper. The estimated value of DH was about 62%. Values of the assayed COD fractions were compared with the same parameters obtained for municipal wastewater by other authors.

A lot of interest has recently been put into the so-called ‘virtual cryptographic currencies’, commonly known as cryptocurrencies, along with its surrounding market. The blockchain technology that stands behind them is also becoming increasingly popular. From the perspective of maintaining energy security, an important issue is the process of mining individual cryptocurrencies, which is associated with very high energy consumption. This operation is usually related to the approval of new blocks in the blockchain network and attaching them to the chain. This process is carried out through performing complex mathematical operations by various devices, which in turn require high power and respectively consume a lot of energy. The impact of cryptocurrency miners on the power and energy demand level might gradually increase over time, therefore this issue shouldn’t be ignored. Comparing the above information in parallel with the growing need for providing demand side response (DSR) services in the Polish Power System, raises the question whether devices used for mining cryptocurrencies can be used for the purpose of balancing the power system. This paper presents an analysis of the possibility to provide the demand side response services by groups of cryptocurrency miners users. The analysis was carried out taking basic functional, technological and economical aspects of these devices’ operations into account.

In cities with large educational institutions, the inflow of educational migrants is important for con-sumption demand, and can trigger multiplier effects. The main aim of this article is to show the mecha-nism of the aggregate demand-income effect created by educational migration in the Polish city of Opole. An estimate of this effect is provided, based on questionnaire research among a sample of 1 075 students from all institutions of higher education located in the city. The estimated effects analysed concern the direct consumption impulse, as well as the indirect job creation and increase in income for providers of accommodation for students, in turn triggering increased consumption demand. While the results must be interpreted with care, an estimated 15 per cent of consumption demand created through expenditure of migrant students (about PLN 175 400 000) and 485 extra job show the significance of such expenditure for the local economy.

The pressure on the use of water and climate change has caused a decreased availability of water resources in semi-arid areas in the last decades. The Setif Province is one of the semi-arid zones of Algeria as it receives an average less than 400 mm∙year–1. The question of the evolution of demographic pressures and their impacts on water resources arise. By applying WEAP software (water evaluation and planning), the aim is to develop a model of water resources management and its uti-lization, assess the proportion of the resource-needs balance and analyse the future situation of water according to different scenarios. This approach allows to identify the most vulnerable sites to climatic and anthropogenic pressures. The estima-tion of the needs for drinking water and wastewater in the Setif Province has shown that these needs increase over time and happening when the offer is not able to cover the demand in a suitable way. It is acknowledged that there is a poor exploita-tion of water resources including underground resources, which translates into unmet demand in all sites of demand.

This article reviews the literature on the relationship between the region’s innovation and its development. Various concepts are discussed in the scheme of the four forces of regional and local competitiveness. The main determinants of the region’s innovation and competitiveness can be viewed in a four-force system: domination forces when the region exploits its advantage over others, network power – when the development potential is strengthened by cooperation, external demand and internal resources. In this framework of literature analysis, the article points to both entities and processes that represent the possibilities of the „innovation being” region.

The paper attempted to define the basis of city transformations that conform to the smart concept. The objective of the paper is to relate the concept of a smart city, which is quite frequently discussed in literature related to the subject, with functioning and development of the city’s economy, in a way that would allow monitoring economic processes taking place in the city, and also to find a response to the question as to the extent to which the smart city creates a new city economy. Does it expand the city economy by new elements, generate new economic mechanisms, allow the implementation of growth paths different than those to date? This objective is particularised by a description of selected issues of urban economics. With this in mind the paper discusses an approach to managing supply and demand on the basis of theoretical assumptions defined by Mudie and Cottam (1993) transposed on realities connected with provision of municipal public services in conditions of a smart city. Furthermore, sample solutions were presented related to the smart city, which reflect theoretical conclusions contained in the paper. The paper ends with a presentation of logics related to growing economy in a smart city. The economy of a smart city, ultimately an intelligent economy of the city, is created in a laminar way. Under the pressure of technological, social and political surroundings the city is permeated by social and culture intelligence, forming gradually a new economic quality. In the paper we emphasised that the concept of a smart city still remains a question of the future to a much bigger extent than one of the present time. A smart city slowly emerges from the combination of diverse megatrends and development trends characteristic for communities and economies of the second decade of the 21st century.

The study of the possibility of removing organic compounds from wastewater originating from the biodiesel purification stage by two catalytic processes, HSO₅^-/transition metal and Fenton method has been presented. The source of the ion HSO₅^- is potassium monopersulphate (2KHSO₅·KHSO₄·K₂SO₄) (Oxone) that may be decomposed into radicals (OH^., SO₄^-., SO₅^-.) by means of transition metal as Co(II). Different concentrations were used for both compounds and the combination ([Co²⁺] = 1.00μM/[HSO₅^-] = 5.00·10^-2 M) achieved the highest COD removal (60%) and complete decomposition of the oxidant was verified for contact times of 45 min. This process has some advantages comparing to the conventional Fenton method such as the absence of the costly pH adjustment and the Fe(III) hydroxide sludge which characterize this treatment process. The Fenton process showed that the combination of [H₂O₂] = 2.00M/[Fe²⁺] = 0.70 M was the best and archived COD removal of 80%. The treatments studied in this research have achieved high COD removal, but the wastewater from the biodiesel purification stage presents very high parametric values of Chemical Oxygen Demand (667,000 mgO₂/L), so the final COD concentration reached is still above the emission limit of discharge in surface water, according the Portuguese Law (Decree-Law 236/98). However, both treatments have proved to be feasible techniques for the pre-oxidation of the wastewater under study and can be considered as a suitable pre-treatment for this type of wastewaters. A rough economic analysis of both processes was, also, made.

The factor which essentially affects sludge biodegradation rate is the degree of fluidization of insoluble organic polymers to the solved form, which is a precondition for availability of nutrients for microorganisms. The phases which substantially limit the rate of anaerobic decomposition include hydrolytic and methanogenic phase.

Subjecting excess sludge to the process of initial disintegration substantially affects the effectiveness of the process of anaerobic stabilization. As a result of intensification of the process of hydrolysis, which manifests itself in the increase in the value and rate of generating volatile fatty acids (VFA), elongation of methanogenic phase of the process and increase in the degree of fermentation of modified sludge can be observed. Use of initial treatment of sewage sludge i.e. thermal disintegration is aimed at breaking microorganisms' cells and release of intracellular organic matter to the liquid phase. As a result of thermal hydrolysis in the sludge, the volatile fatty acids (VFA) are generated as early as at the stage of the process of conditioning. The obtained value of VFA determines the course of biological hydrolysis which is the first phase of anaerobic stabilization.

The aim of the present study was to determine the effect of thermal disintegration of excess sludge on the effectiveness of the process of hydrolysis in anaerobic stabilization i.e. the rate of production of volatile fatty acids, changes in the level of chemical oxygen demand (COD) and increase in the degree of reduction in organic matter. During the first stage of the investigations, the most favourable conditions of thermal disintegration of excess sludge were identified using the temperatures of 50°C, 70°C, 90°C and heating times of 1.5 h - 6 h. The sludge was placed in laboratory flasks secured with a glass plug with liquid-column gauge and subjected to thermal treatment in water bath with shaker option. Another stage involved 8-day process of anaerobic stabilization of raw and thermally disintegrated excess sludge. Stabilization was carried out in mesophilic temperature regime i.e. at 37°C, under periodical conditions. In the case of the process of anaerobic stabilization of thermally disintegrated excess sludge at the temperature of 50°C and heating time of 6 h (mixture B) and 70°C and heating time of 4.5% (mixture C), the degree of fermentation of 30.67% and 33.63%, respectively, was obtained. For the studied sludge, i.e. mixture B and mixture C, maximal level of volatile fatty acids i.e. 874.29 mg CH3COOH/dm3 and 1131.43 mg CH3COOH/dm3 was found on the 2nd day of the process. The maximal obtained value of VFA was correlated on this day with maximal COD level, which was 1344 mg O2/dm3 for mixture B and 1778 mg O2/dm3 for mixture C.