Municipal wastewater sludge was produced by chemical coagulation of synthetic wastewater (sww) based on Synthene Scarlet P3GL disperse dye and real municipal wastewater (nww), coagulated by commercial coagulants PAX (prepolymerised aluminum coagulant) and PIX (a ferric coagulant based on Fe2(SO4)3). An attempt was made to correlate the sludge’s dewatering capacity (in terms of capillary suction time—CST) with operation parameters for wastewater treatment, size distribution and specific surface area of the sludge particles. It was found that the presence of phosphate ions in the system facilitates the removal efficiency of the above-mentioned dye (L) due to the interaction between the dye molecules and H2PO4− ions. Unlike sww, negatively charged organic substances (sorg) in nww are directly adsorbed on the surface of colloidal particles {Fe(OH)3} and {Al(OH)3} (prtc). It was also discovered that an increase in the dose of a coagulant led to an increase of CST for sww sludge and to a decrease of CST for nww sludge. It has been suggested that flocs composed of spherical {Al(OH)3} units possessed more internal space for water than aggregates consisting of rod-shaped {Fe(OH)3} units and, consequently, it is more difficult to remove water from Al-sww sludge than from Fe-sww. The results obtained showed that smaller particles dominate in sww sludge, while larger particles are prevalent in nww sludge. To explain this distinct difference in the size distribution of particles in sludge obtained with the use of Al3+ and Fe3+, simple models of aggregation and agglomeration-flocculation processes (aaf) of treated wastewater have been proposed. Except for PIX in nww, the analyzed particles of the investigated types of sludge were characterized by similar specific surface area (Sps), regardless of the kind of sludge or the applied coagulant. Slightly larger, negatively-charged sorg bridges, anchored directly on the surface of positive prtc are more effective in closing the structure of nww sludge than small L bridges of the dye molecules anchored on the surface of prtc via H2PO4−. All the discovered aspects could lead to improved performance of wastewater treatment plants (WWTP) by increasing the efficiency of sludge dewatering.

a b s t r a c tIn this study, a pilot test of electrocoagulation (EC with aluminium electrodes) of natural municipal wastewater was performed. In view of the obtained results and the unique and innovative nature of the proposed procedures and solutions, EC can be regarded not only as a preliminary purification step, but also as a comprehensive alternative to other wastewater treatment methods. Electrocoagulation was conducted at constant current, and changes in voltage were registered continuously to control and calculate energy consumption. After 2 h (7200 s of EC + 1800 s of additional sludge settling), initial colour (2140-2570 mg/L) was removed in 86-99.5%, turbidity (87.5-149 mg/L) -in 100%, suspended solids (250-340 mg/L) -in 88.5-91%, COD (609-737 mg/L) -in 60.8-63.5%, and phosphorus (10.0-10.7 mg/L) -in 94.5-96%. As expected, a higher electrocoagulant dose at higher energy consumption improved the efficiency of wastewater treatment, but energy consumption was not directly proportional to the treatment efficiencies of electrocoagulated municipal wastewater. The obtained results of sewage purification seem to be promising both economically and technologically. They fulfil Polish standards of effluent quality, except for COD where higher efficiency is required. EC poses a viable alternative to other wastewater treatment methods and should be considered as an initial step in municipal wastewater treatment.

The novel automatic flow system, direct-injection detector (DID) integrated with multi-pumping flow system (MPFS), dedicated for the photometric determination of orthophosphates in wastewater and freshwater samples is for the first time described. All reagents and the sample were injected simultaneously, in counter-current into the reaction-detection chamber by the system of specially selected for this purpose solenoid micro-pumps. The micro-pumps provided good precision and accuracy of the injected volumes. For the determination of orthophosphates, the molybdenum blue method was employed. The developed method can be used to detect orthophosphate in the range 0.1–12 mg L−1, with the repeatability (RSD) about 2.2% at 4 mg L−1 and a very high injection throughput of 120 injections h−1. It was possible to achieve a very small consumption of reagents (10 μL of ammonium molybdate and 10 μL of ascorbic acid) and sample (20 μL). The volume of generated waste was only 440 μL per analysis. The method has been successfully applied, giving a good accuracy, to determination of orthophosphates in complex matrix samples: treated wastewater, lake water and reference sample of groundwater. The developed system is compact, small in both size and weight, requires 12 V in supply voltage, which are desirable for truly portable equipment used in routine analysis. The simplicity of the system should result in its greater long-time reliability comparing to other flow methods previously described.