Chloramination of drinking water and wastewater can generate carcinogenic nitrosamines, among which, nitrosodipropylamine (NDPA) with large molecular weight and weak polarity has been commonly found. However, knowledge on the formation of NDPA remains highly limited. Laboratory tests were conducted to quantify NDPA formation during chloramination of nitrogenous precursors, including dipropylamine and methyldipropylamine, and pesticides such as trifluralin, oryzalin, and vernolat. Results showed that all precursors exhibited > 10.0% NDPA yields after 24 h. Oryzalin and trifluralin accomplished the highest (13.63%) and lowest (11.31%) yield, respectively. Maximal yields of all precursors were observed at pH 9.0 and temperature 288 K. Maximums of NDPA yield from oryzalin (18.27%) and vernolat (19.54%) were formed at Cl:N of 0.7:1.0, but maximal yields of dipropylamine (18.44%), methyldipropylamine (22.98%), and trifluralin (33.06%) were achieved at Cl:N of 1.2:1.0. Maximal NDPA yields of dipropylamine (37.14%), methyldipropylamine (32.84%), and vernolat (49.02%) were observed at [NH₂Cl]₀:[precursor]₀ = 500, but highest yields of trifluralin (30.24%) and oryzalin (25.53%) were accomplished at [NH₂Cl]₀:[precursor]₀ = 50. Bromide and organic contents in tap and raw water reduced NDPA due to competition for NH₂Cl. Chloramination of water impacted by amines and pesticides should be careful of NDPA formation.

Pre-oxidation in water treatment is considered an effective method to enhance the removal of algal cells and their exuded organic matters. However, pre-oxidation also alters the characteristics of algae and consequently influences disinfection processes. The existing studies mainly focused on the stationary growth phase, but little is known for the exponential and declined phases. The objectives of this study were to examine the effects of pre-ozonation on the integrity of algal cells, the release of algal organic matters, and the formation of disinfection by-products like N-nitrosodimethylamine (NDMA) from Microcystis aeruginosa (M. aeruginosa) at three growth phases. The results demonstrated that pre-ozonation was efficient to inactivate M. aeruginosa cells. The severity of M. aeruginosa cell damage increased as the ozone dosage increased from 0.5 to 2.0 mg/L. The damage of cell membranes resulted in the release of intracellular organic matters. Excitation-emission matrix spectra (EEMS) analysis indicated that ozone mainly reacted with soluble microbial products (SMP). With the increase of ozone concentration, although the trend of NDMA formation was similar for all three growth phases, more production of NDMA by algal cells was observed at the declined phase. In the post-disinfection process, chloramine showed the potential as a more suitable disinfectant than chlorination after pre-ozonation to minimize the NDMA formation. Therefore, appropriate pre-ozonation is beneficial to reduce the NDMA formation from exponential algae, while has no significant change during both stationary and declined phases.

The availability of clean water from the already scarce sources is threatened by continuous addition of contaminated industrial and of abattoir waste into watercourses globally. The aim of the current study was to reduce the amount of waste produced, to decrease pollution derived from discharge of effluent meat wastewater, and also to minimise environmental health risk. This was all achieved by successfully synthesising a natural biopolymer chitin chitin-chitosan derivative derived from crab shell waste. Characterisation of the chitin polymer using physicochemical properties like yield, ash content, degree of acetylation, solubility, intrinsic viscosity, and molecular weight indicated that crab shell waste was a good source of chitin. This polymer was later deacetylated to form chitosan and then cross-linked with s-methylbutylamine to form chitin-chitosan adsorbent. The effectiveness of the above-modified product in purifying meat wastewater was conducted by means of comparative testing using hydride gas atomic absorption spectroscopy. The results of the qualitative and quantitative analysis showed that chitosan cross-linked s-methylbutylamine was efficient in removing the following metal ions: Cu (II), Zn (II), Cr (II), Pb (II), and Cr (II). The highest removal percentage was Cr (IV) and Pb (II) (95.45 and 92.66%), while Zn (II) and Fe (II) were 87.32 and 67.48%. The lowest percentage recovery of 38.55% was observed for the metal Cr. From the current study, it was evident that the cross-linked can significantly reduce the metal concentration in meat wastewater before it is released in the aquatic environment. Therefore, properly permitted international waste disposal methods should be employed to reduce adverse effects on the receiving environment.