Dr 3900 spectrophotometer

Concentrations of COD, TN, N–NH₄⁺, N–NO₂⁻, N–NO₃⁻, P-PO₄³⁻ were analysed spectrometrically according to APHA Standard Methods (APHA 2005 ) using cuvette tests (Hach Lange GmbH) and a DR 3900 spectrophotometer (Hach Lange GmbH, Berlin, Germany). The determination of mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) employed gravimetric methods in accordance with Polish standard PN-EN 872:2007. Measurement of total volatile solids in biofilm was performed in accordance with the Polish standard by calculating weight loss. The biofilm was mechanically removed from the carries.
Free ammonia (FA) and free nitrous acid (FNA) were calculated according to Eqs. (3) and (4) (Anthonisen et al. 1976 (link)) $$\text{FA}=\frac{17}{14}\times \frac{\text{total}\text{ammonia}\text{as}\text{N}\left(\frac{\text{mg}}{\text{L}}\right)\times {10}^{\text{pH}}}{{\text{e}}^{\left(6344/273+{\text{T}}^{\circ }\text{C}\right)}+{10}^{\text{pH}}}\left[\text{mgFA}/\text{L}\right]$$ $$\text{FNA}=\frac{46}{14}\times \frac{\text{N}-{\text{NO}}_2^{-}\left(\frac{\text{mg}}{\text{L}}\right)}{{\text{e}}^{\left(-2300/273+{\text{T}}^{\circ }\text{C}\right)}\times {10}^{\text{pH}}}\left[\text{mgFNA}/\text{L}\right]$$

An element of known weight was placed in a solution with copper content of 5 mg/L. After specified time intervals, samples were taken and the content of copper ions was determined again. Tests for the content of copper ions were performed using Hach Lange cuvette tests: LCK329 and a dedicated Hach Lange DR 3900 spectrophotometer (Düsseldorf, Germany). Based on the loss of Cu ions, the degree of their adsorption on the tested elements was determined.

The treatment efficiency was assessed based on the change in the chemical oxygen demand (COD) index during one cycle, which was calculated according to the following formula: $$\mathrm{E}=\frac{{COD}_1-{COD}_2}{{COD}_1}\ast 100 [\%]$$
where:

COD₁—chemical oxygen demand at the beginning of the cycle [mg/LO₂];

COD₂—chemical oxygen demand at the end of the cycle [mg/LO₂].

COD tests were performed using Hach Lange cuvette tests: LCK114, LCK314 and a dedicated Hach Lange DR 3900 spectrophotometer (Düsseldorf, Germany).

Metal ion adsorption study was performed for bio-sorbents chitosan and binary matrices by equilibration method. The standard solutions of metal ions having concentration $5.00$ mg/L for the respective metal ions were made by the dissolution of calculated weights of $FeS{O}_4$ , $7H_{2}O$ and $Pb{\left(N{O}_3\right)}_2$ in deionized water. For the sorption studies 250 mg of polymer samples were dipped in $10.00$ mL metal ion solution (only single metal ion) at particular contact time, pH, temperature and fed metal ion concentration one by one to evaluate the optimum conditions of contact time, temperature, pH and metal ion feed concentration. The solution was observed for the rejected ions concentration on DR 3900 Spectrophotometer (HACH Co., Loveland, CO, USA) by using standard pillow reagents. Parameter contact time, pH, temperature and individually fed metal ion concentration were varied one by one in order to evaluate optimum sorption conditions [32 (link)]. Metal ion sorption parameters such as retention capacity ( $Q_r$ ), percent uptake ( $P_u$ ) as well as partition coefficient ( $K_d$ ) were calculated as follows ((3)–(5)): $$P_u=\frac{C_o-P_r}{C_o}\times 100,$$
$$K_d=\frac{C_a}{C_r}\times \frac{V\left(mL\right)}{W_p\left(g\right)},$$
$$Q_r=\frac{C_a\left(mEQ\right)}{W_p\left(g\right)},$$
where:

Co is fed metal ions concentration,

Cr is rejected metal ions concentration,

Ca is metal ions concentration ion in polymeric matrix,

V is solution volume in mL,

Wp is dry polymeric weight in grams.

Cultures of each strain were harvested in exponential growth phase by centrifugation (6 min, 3700g), washed repeatedly with the treated wastewater medium, and resuspended in it. Initial cultures for the experiments were then prepared by adjusting the optical density (OD₆₃₀) of the suspensions to 0.06 and placing 60 mL aliquots in tubes designed to fit slots in a MC 1000 multi-cultivator (Photon System Instruments, Drásov, Czech Republic). Each species was grown in triplicates at 50, 150 and 300 μE m⁻² s⁻¹ (16 h light: 8 h dark photoperiod). The temperature was 25 ± 2 °C and the tubes were aerated (0.1 L min⁻¹). The algae were grown under these conditions for either 8 or 15 days, and OD₆₃₀ was measured daily to monitor their growth. Samples (50 mL) were then harvested by centrifugation at 3700 g for 6 min and freeze-dried for 3 days. Freeze-dried algae were used for lipid extraction and FTIRS analysis. The amounts of nitrogen and phosphorus present in the wastewater were determined before and after each experiment using LCK 138 and LCK349 kits, respectively, and a DR 3900 spectrophotometer, operated according to the manufacturer’s manual (Hach Lange, Germany).