Agrotechnical assessment of struvite produced by a lab-scale sedimentation unit is performed. As a source of phosphates and ammonia, liquor obtained through dewatering of Мunicipal wastewater treatment plant sludge was in use. The range of phosphates and ammonia was in the range of 130 -250 and 380 -560 mg/L, respectively. Seawater brine with a magnesium concentration of around 60 g Mg 2+ /L was applied as a source of magnesium. The agrotechnical characteristics of struvite obtained were compared to ammonium nitrate and carbamide in regards to the productivity effects on maize hybrid P9241. The results show that the effectiveness of struvite and some commercial fertilizers is quite close. The highest yield in the experiment was achieved with the application of carbamide plus ammonium nitrate (56.64 kg/ha), while in applying struvite solely it is 54.60 kg/ha. The highest protein content of maize (9.7%) was observed in the case of struvite/ammonium nitrate application.

The high concentration of phosphorus and nitrogen in wastewater and sludge could be lowered to a certain level by struvite (MgNH4PO4•6H2O) crystallization. One of the main factors for struvite formation is the solution pH. It can be adjusted by non-reagent carbon (CO2) dioxide stripping through the process of aeration. The intensity of the mass transfer between the air and the supernatant of dewatering sludge obtained from wastewater treatment plant is characterized by the volumetric liquid-side mass transfer coefficient, which can be estimated theoretically. It is found that the rate of pH increase depends strongly on the sparging area of the air distribution system while the air flow rate does not influence considerably the Dissolved Oxygen (DO) level which governs the CO2 stripping process. The theoretical calculated values of the volumetric mass transfer coefficient have been compared with those obtained experimentally. Based on the data obtained, relationships of pH/kLa (mass transfer coefficient) were developed. These correlations serve as a tool for prediction of pH during the struvite precipitation process.

The paper gives information on the depletion of phosphorus (P) as an important element for all forms of life and its pollution impact on the environment in case of intensive discharge of phosphorus compounds into water bodies. Two secondary waste sources of Phosphorus are under consideration, namely the domestic wastewater and sludge and animal manure. The characteristics of these two fluids regarding organic matter and nutrient content are summarized. Discussing the techniques for P extraction mostly attention is given to phosphorus precipitation as ammonium magnesium phosphate (struvite). Examples of effectiveness of P precipitation as struvite in Municipal Wastewater Treatment Plants (MWWTPs) with chemical and biological P removal are presented. The examples of struvite production from sewage and manure waste show evidently the great potential of utilization of such a waste as a source of phosphorus. The recovered product is valuable both as it is a slow release fertilizer and with its low content of heavy metals compared to the mineral fertilizers. In respect of the diminishing amount of natural P rocks, the sewagec wastewater and sludge and the animal manure can be regarded as an important secondary source of Phosphorus.

Two options, in regard to applying microbial fuel cells (MFCs) in water treatment, are under discussion, namely the conversion of the chemical energy of organic substrates to electricity, as well as the use their potential to reduce different species, such as the ionic form of copper (Cu2+ converted to metal copper) and iron (Fe3+ converted to Fe2+). The high reduction potential of Cu2+ and Fe3+ makes the processes of electricity production and metal reduction, to be performed simultaneously in MFC, achievable. The electrical yield measurement during the experiments of anodic organic matter degradation by MFC in treating an artificial wastewater with chemical oxygen demand (COD) 0.6 and 1.6 g O2·dm−3, as initial COD, are given. It is demonstrated that the higher organic load is associated with better electrical yield. A comparison of MFC and conventional anaerobic digestion performance is discussed, as well. Experimental proofs of copper removal and phosphate mobilization, following the iron reduction of FePO4, are also reported.

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