Analytical techniques to measure organic matter in water, such as Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD₅), and Total Organic Carbon (TOC) are widely used. Modifications have been proposed to make them faster, more sensitive, and more environmentally friendly. The purpose of producing a review over some time is to show the changes made on the standardized methods of each of these techniques, and to highlight the relationship between them in the process of ascertaining organic matter in water. Modifications to techniques COD and BOD entail several factors that need to be considered, namely: time, miniaturization, sensitivity, use of environmentally friendly reagents. Changes to TOC are focused on detection systems. Despite the advantages obtained by the modified techniques, traditional methods continue to be widely used, in most cases due to the lack of standardization of the new methods. Graphic Abstract

A green method for synthesizing iron oxide nanorods within orange peel pith has been developed. Orange peel pith functions as both a support and a reducing agent for iron ions. The nanorods were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Results of the characterization indicate that iron is deposited on the surface of orange peel primarily in the form of iron, iron(II) oxide and magnetite. The nanoparticles grow to form nanorods in the range of 20–40 nm of diameter. The biocomposite was then tested for Cr(VI) reduction and removal from aqueous solutions, exhibiting removals as high as 96% for concentrations of 10 mg/L and 76% for 50 mg/L, which is almost 4 times the removal capacity of orange peel alone.