Chemical oxygen demand (COD) is a practical parameter that is used to estimate the amount of organic pollutants in aqueous systems It is generally used as a guideline to control the quality of waste treatment effluent globally and is a management tool to evaluate the total pollution load in the highly developed coastal regions of Korea It is a preferred method because of the speed and simplicity of the analysis and because there are fewer instrumentation requirements The Ministry of Oceans and Fisheries (MOF) of the Republic of Korea developed a standard procedure for the measurement of COD It has been revised several times, and the most recent revision was made in 2013 (MOF 2013–230) In this study, we modified the standard COD measurement procedure (MOF 2013–230), especially the sample digestion apparatus, to enhance analytical efficiency for a large sample number (batch), which is called a Korea Institute of Ocean Science and Technology (KIOST) modified MOF 2013–230 We examined uncertainty related to each experimental step and optimized laboratory conditions to reduce such uncertainties The detection limit and estimated expanded uncertainty related to the KIOST modified MOF 2013–230 was 018 and 011 mg O2/L at a 95% confidence level (k = 2), respectively This study also provides several tips to maintain consistent COD measurements in seawater using the alkaline potassium permanganate method

Optimization of Chemical Oxygen Demand Determination in Seawater Samples Using the Alkaline Potassium Permanganate Method

The marine microalgae Tetraselmis striata was cultivated in drilling waters with different salinities. Growth substrate optimization was performed while the effects of different pH, temperature, photoperiod and CO2 flow rate on biomass productivity and its composition were studied. Results showed that the strain grew better in 2.8% drilling waters employing the fertilizer Nutri-Leaf together with ΝaHCO3. A pH value of 8 resulted in high biomass productivity (79.8 mg L−1 d−1) and biomass composition (proteins 51.2% d.w., carbohydrates 14.6% d.w., lipids 27.8% d.w. and total chlorophylls 5.1% d.w.). The optimum cultivation temperature was found to be 25 ± 1 °C which further enhanced biomass productivity (93.7 mg L−1 d−1) and composition (proteins 38.7% d.w., carbohydrates 20.4% d.w., lipids 30.2% d.w., total chlorophylls 5.1% d.w.). Photoperiod experiments showed that continuous illumination was essential for biomass production. A 10 mL min−1 flow rate of CO2 lead to biomass productivity of 87.5 mg L−1 d−1 and high intracellular content (proteins 44.6% d.w., carbohydrates 10.3% d.w., lipids 27.3% d.w., total chlorophylls 5.2% d.w.). Applying the optimum growth conditions, the produced biomass presented high protein content with adequate amino acids and high percentages of eicosapentaenoic acid (EPA), indicating its suitability for incorporation into conventional fish feeds. In addition, this study analyzed how functional parameters may influence the uptake of nutrients by Tetraselmis.

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Optimization of Cultivation Conditions for Tetraselmis striata and Biomass Quality Evaluation for Fish Feed Production

Marine microalgae are considered an important feedstock of multiple valuable metabolic compounds of high biotechnological potential. In this work, the marine microalga Tetraselmis striata was cultivated in different scaled photobioreactors (PBRs). Initially, experiments were performed using two different growth substrates (a modified F/2 and the commercial fertilizer Nutri-Leaf (30% TN—10% P—10% K)) to identify the most efficient and low-cost growth medium. These experiments took place in 4 L glass aquariums at the laboratory scale and in a 9 L vertical tubular pilot column. Enhanced biomass productivities (up to 83.2 mg L−1 d−1) and improved biomass composition (up to 41.8% d.w. proteins, 18.7% d.w. carbohydrates, 25.7% d.w. lipids and 4.2% d.w. total chlorophylls) were found when the fertilizer was used. Pilot-scale experiments were then performed using Nutri-Leaf as a growth medium in different PBRs: (a) a paddle wheel, open, raceway pond of 40 L, and (b) a disposable polyethylene (plastic) bag of 280 L working volume. Biomass growth and composition were also monitored at the pilot scale, showing that high-quality biomass can be produced, with important lipids (up to 27.6% d.w.), protein (up to 45.3% d.w.), carbohydrate (up to 15.5% d.w.) and pigment contents (up to 4.2% d.w. total chlorophylls), and high percentages of eicosapentaenoic acid (EPA). The research revealed that the strain successfully escalated in larger volumes and the biochemical composition of its biomass presents high commercial interest and could potentially be used as a feed ingredient.

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Laboratory- and Pilot-Scale Cultivation of Tetraselmis striata to Produce Valuable Metabolic Compounds

A modified method for the determination of the chemical oxygen demand in sea water is presented in this paper. The proposed method differs from the alternate method for low COD samples described in the 17th edition of the Standard Methods for the Examination of Water and Wastewater in that it employs a pretreatment step resulting in complete halides removal from the sea water sample. Complete removal of halides is realised by adding 3 g silver sulphate per 30 ml sea water sample in a 50 ml erlenmeyer flask and mixing for 60- 90 min (when a fade lilac colour appears) followed by settling of the precipitates formed for 5-10 min with the flask in a 40 ° inclined position and finally taking slowly and with care the volume of the cleared sea water required for the COD test with a volumetric pipette.

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S.P. Tsonis

Papers

A Modified Method For The Determination OfChemical Oxygen Demand In Sea Water