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This manuscript presents results of a study on sorption effectiveness of orthophosphate and nitrate III and V in an equimolar mixture of P–PO 4 , N–NO 2 and N–NO 3 using chitosan in the form of hydrogel beads. Analyses were carried out for: the effect of pH on sorption intensity of orthophosphate and of nitrate III and V onto chitosan, sorption kinetics onto chitosan, and the maximum sorption capacity of P–PO 4 , N–NO 2 and N–NO 3 by chitosan in a mixture. The most effective sorption of P–PO 4 , N–NO 2 and N–NO 3 was observed at pH 4. In turn, at pH 6–11 the sorption of orthophosphate and nitrate onto chitosan proved ineffective. P–PO 4 , N–NO 2 and N–NO 3 sorption kinetics was best described by the pseudo-second order model. The model of intraparticle diffusion fitting to experimental data demonstrated that the process of orthophosphate and nitrate sorption onto chitosan proceeded in 2 phases, i.e. 1 – adsorption and 2 – absorption. A phenomenon of the partial release of P–PO 4 , N–NO 2 and N–NO 3 after a specified period of time was observed in the study, which was due to a change in solution pH induced by the sorbent. The period after which desorption occurred was 120 min in the case of phosphates and 60 min in the case of nitrates III and V. The quantity of bound sorbate (a mixture of orthophosphate and nitrate) was the highest in the 60th minute of sorption. The study demonstrated evident competition between H 2 PO 4 − , NO 2 − and NO 3 − ions. The affinity of orthophosphate and nitrate to the sorption centers of chitosan could be ordered as follows: P – PO 4 > N – NO 2 > N – NO 3 . Sorption equilibrium isotherms were best described by a heterogeneous Langmuir’s model. In the equimolar mixture of P–PO 4 , N–NO 2 and N–NO 3 , the sorption capacity of 1 g of chitosan reached 0.507 mmol H 2 PO 4 − /g, 0.373 mmol NO 2 − /g and 0.350 mmol NO 3 − /g, which means a total of 1.23 mmol nutrients.

A hydrogel chitosan sorbent ionically cross-linked with sodium citrate and covalently cross-linked with epichlorohydrin was used to remove nutrients from an equimolar mixture of P-PO4, N-NO2 and N-NO3. The scope of the study included, among other things, determination of the influence of pH on nutrient sorption effectiveness, nutrient sorption kinetics as well as determination of the maximum sorption capacity of cross-linked chitosan sorbents regarding P-PO4 (H2PO4-, HPO42-), N-NO2 (HNO2, NO2-), and N-NO3 (NO3-). The effect of the type of the cross-linking agent on the affinity of the modified chitosan to each nutrient was studied as well. The kinetics of nutrient sorption on the tested chitosan sorbents was best described with the pseudo-second order model. The model of intramolecular diffusion showed that P-PO4, N-NO2 and N-NO3 sorption on cross-linked hydrogel chitosan beads proceeded in two phases. The best sorbent of nutrients turned out to be chitosan cross-linked covalently with epichlorohydrin; with P-PO4, N-NO2 and N-NO3 sorption capacity reaching: 1.23, 0.94 and 0.76mmol/g, respectively (total of 2.92mmol/g). For comparison, the sorption capacity of chitosan cross-linked ionically with sodium citrate was: 0.43, 0.39 and 0.39mmol/g for P-PO4, N-NO2 and N-NO3, respectively (total of 1.21mmol/g).

This study compared properties of hydrogel chitosan sorbents crosslinked with eight agents, including four ionic ones: sodium citrate, sodium tripolyphosphate, sulfosuccinic acid, and oxalic acid and four covalent ones: glutaraldehyde, epichlorohydrin, trimethylpropane triglycidyl ether, and ethylene glycol diglycidyl ether. The effect of crosslinking process conditions (pH, temperature) and dose of the crosslinking agent on chitosan sorbent stability during sorption and on the effectiveness of Reactive Black 5 dye sorption were examined. The optimal parameters of crosslinking ensuring sorbent stability in acidic solutions and high sorption capability were established for each crosslinking agent tested. The susceptibility of crosslinked sorbents to mechanical damages was analyzed as well. The process of ionic crosslinking was the most effective at the pH value below which hydrogel chitosan sorbent began to dissolve (pH 4). The crosslinking temperature ranging from 25 to 60 °C had no effect upon sorbent stability. The higher temperature during ionic crosslinking, however, slightly decreased RB5 sorption effectiveness. The ionic crosslinking significantly decrease the susceptibility of chitosan hydrogels to mechanical damages. In the case of covalent crosslinking of chitosan hydrogel beads, the effect of process conditions (pH, temperature) on the properties of the crosslinked sorbent depended on the type of crosslinking agent. The sorbents crosslinked with covalent agents were usually harder but also more fragile, and therefore more susceptible to mechanical damages.

The article presents the effectiveness of phosphate sorption on the unmodified and modified (animation from the initial activation by epichlorohydrin) husks Arachis hypogaea. Studies performed determined dose activating agent (epichlorohydrin), adsorption capacity of unmodified and modified husks Arachis hypogaea, best among the tested adsorption pH as well as the equilibrium time. Langmuir model was used to describe the results. The highest removal efficiency of phosphorus compounds using unmodified husks Arachis hypogaea was obtained at pH 8, and with aminated at pH 5. The study of phosphate equilibrium concentration time obtained for both sorbents was carried out at three concentrations of 0,1; 0,5 and 1 mg/L. The highest sorption efficiency of the phosphate onto both sorbents was achieved after 60 minutes of the process. After the equilibrium time the effect of partial nutritient release was observed, which could be related to the change in pH of the solution by the sorbent. Studies have shown that the modification consists in the amination of husks Arachis hypogaea with pre-activated with epichlorohydrin increases their effectiveness removal of phosphorus compounds. The maximum adsorption capacity of unmodified husks with towards phosphate was 0.011 mg/g, while the husks animated with initial activation – 0.10 mg/g.

In this study the effectiveness of sorption Basic Violet 10 were examined (the popular in the industry cationic dye), on 6 different non-conventional sorbents: chitin, sawdust, compost, silage corn, zeolite and fly ash. For each test sorbent was determined optimum pH of sorption. Was also a designated the maximum sorption capacity with respect to the Basic Violet 10. The results obtained were analyzed with the use of three sorption isotherms: Freundlich, Langmuir and double Langmuir. Among the organic sorbents tested, the highest capacity relative to Basic Violet 10 shown sawdust (Qmax = 156.5 mg/g) and corn silage (Qmax = 180.8 mg/g). In the case of mineral sorbents such as zeolite or fly ash, the maximum absorptive capacity Basic Violet 10 was respectively Qmax = 144.1 mg/g and 170.1 mg/g.

A series of investigations were conducted using sequencing batch biofilm reactor (SBBR) to explore the influence of C:N:P ratio on biological dephosphatation including the denitrifying dephosphatation and the denitrification process. Biomass in the reactor occurred mainly in the form of a biofilm attached to completely submerged disks. Acetic acid was used as the source of organic carbon. C:N:P ratios have had a significant effect on the profiles of phosphate release and phosphate uptake and nitrogen removal. The highest rates of phosphate release and phosphate uptake were recorded at the C:N:P ratio of 140:70:7. The C:N ratio of 2.5:1 ensured complete denitrification. The highest rate of denitrification was achieved at the C:N:P ratio of 140:35:7. The increase of nitrogen load caused an increase in phosphates removal until a ratio C:N:P of 140:140:7. Bacteria of the biofilm exposed to alternate conditions of mixing and aeration exhibited enhanced intracellular accumulation of polyphosphates. Also, the structure of the biofilm encouraged anaerobic-aerobic as well as anoxic-anaerobic and absolutely anaerobic conditions in a SBBR. These heterogeneous conditions in the presence of nitrates may be a significant factor determining the promotion of denitrifying polyphosphate accumulating organism (DNPAO) development.

We investigated cadmium sorption by activated sludge immobilized in 1.5% sodium alginate with 0.5% polyvinyl alcohol. Experiments were conducted in an air-lift type reactor at the constant concentration of biosorbent reaching 5 d.m./dm3, at three flow rates: 0.1, 0.25 and 0.5 V/h, and at three concentrations of the inflowing cadmium solution: 10, 25 and 50mg/dm3. Analyses determined adsorption capacity of activated sludge immobilized in alginate as well as reactor’s work time depending on flow rate and initial concentration of the solution. Results achieved were described with the use of Thomas model. The highest adsorption capacity of the sorbent (determined from the Thomas model), i.e., 200.2 mg/g d.m. was obtained at inflowing solution concentration of 50 mg/dm3 and flow rate of 0.1 V/h, whereas the lowest one reached 53.69 mg/g d.m. at the respective values of 10 mg/dm3 and 0.1 V/h. Analyses were also carried out to determine the degree of biosorbent adsorption capacity utilization at the assumed effectiveness of cadmium removal — at the breakthrough point (C=0.05*C0) and at adsorption capacity depletion point (C-0.9*C0). The study demonstrated that the effectiveness of adsorption capacity utilization was influenced by both the concentration and flow rate of the inflowing solution. The highest degree of sorbent capacity utilization was noted at inflowing solution concentration of 50 mg/dm3 and flow rate of 0.1 V/h, whereas the lowest one at the respective values of 10 mg/dm3 and 0.1 V/h. The course of the process under dynamic conditions was evaluated using coefficients of tangent inclination — a, at point C/C0=½. A distinct tendency was demonstrated in changes of tangent slope a as affected by the initial concentration of cadmium and flow rate of the solution. The highest values of a coefficient were achieved at the flow rate of 0.1 V/h and initial cadmium concentration of 50 mg/dm3.

A hydrogel chitosan sorbent ionically cross-linked with sodium citrate and covalently cross-linked with epichlorohydrin was used to remove nutrients from an equimolar mixture of P-PO