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This article investigates the efficiency of phosphorus removal in the municipal wastewater treatment plants in five counties of Romania from 2013 to 2017. This study focused on evaluation of the performance of phosphorus elimination using biological methods in order to respect the admissible effluent discharge limits. The yearly average of inflow total phosphorus varies from 3.64 mg/L to 4.22 mg/L comparing with 1.02 mg/ L and 1.59 mg/L the average of outflow. Chemical and biological methods are utilized to remove phosphorus. The efficiency of the numerous process available for the phosphorus removal is quite inadequate by comparing the effluent degree of purification and the removal cost.

The compressor rotors usually are helical surfaces with constant pitch and are composed crossing profiles. Frequently, for repair operations occurs the reconstruction necessity for one or both of the worms, drive and driven, from the helical compressors gear. The helical composed surface of rotor flank is generated usually with side mill. The knowledge of worm shape can not be made from geometrical conditions. In these conditions it is necessary to determine the flank form by actual measuring the crossing profiles of these parts. So, the theoretical helical surface of the worm is being substituted by an assembly of helical lines which together with crossing profiles forms points cloud resulted from measuring leads to a polyhedral expression of the flank rotor. Numerically, this surface type is expressed by a coordinate array which shows its discrete image. The profiling of cutting tool bounded by a revolution surface reciprocally enveloping with the substitutive surface of the helical one represents a special problem. In this paper is proposed an algorithm for polyhedral expression of the helical surface previously determined by reverse engineering methods and an algorithm for the determination of the specific enveloping condition at contact with a discrete surface.It is presented an example for a compressor rotor measured on a 3D measuring machine, the algorithm for the transformation of the gathered points cloud in a surface with polyhedral expression. Given these conditions there were determined the enveloping condition and the axial section of the side mill.

Cryogenic air separation units are widely used in industry, which consume a large energy and need to produce a huge amount of need of nitrogen, oxygen and argon products with high purity. High purity distillation columns are critical unit operations in cryogenic air separation plants. In this paper the low pressure distillation column is investigated by using a steady state model. The first principles mathematic model of the column is firstly developed, and the pressure, temperature and static liquid nitrogen, oxygen and argon concentrations in the upper column are presented. The obtained results give important information on the variation of temperature, pressure, component concentrations and molar flows within the distillation column. The study highlighted the importance of considering air as ternary mixture. The separation process performance is significantly influenced by the location of side draw of argon and reflux ratio at the top of the column

Helical rotors, components of screw compressors have different structural shapes: rotors circular front section, rotors elliptic front section or asymmetric rotors. Manufacturing rotors involves profiling a tool bordered by a revolution surface, enveloping of each helical channel. This paper proposes a method developed in AutoCAD, in order to determine the profile of end mill cutter which generates the helical channel. Graphic method is based on the principle of complementary theorems' "Substitute Circles Family Method" component of envelope surfaces theory.