Natural Organic Matter Removal Efficiency Research Articles

Effect of natural organic compounds on the removal of organic carbon in coagulation and flocculation processes

Natural organic matter (NOM) in water contains organic compounds that are both hydrophobic and hydrophilic with a wide range of molecular weights. It is composed of non-homogeneous organic compounds such as humic substances, amino acids, sugars, aliphatic and aromatic acids, and other chemical synthetic organic matters. NOM in water is a major concern not only because of its contribution to the formation of disinfection by-products (DBPs) and taste and odor, but also its influence on the demand for coagulants and disinfectants, the removal efficiency of water treatment processes, etc. This research aims at identifying the influence of NOM in coagulation and flocculation processes in order to optimize the coagulation and flocculation conditions. In this study, pretreated pond water was used as the source water. It was observed from the experimental results that:The optimum pH for coagulation to remove NOM is around 7.The optimum alum dose at this pH can vary from 125-1,225 mgl-1 when the TOC is increased from 4 to 25 mgl-1.The presence of secondary compounds such as Ca2+, Mg2+ divalent cations had no significant effect on the removal of organic matter.The presence of clay increased the organic removal by 15%.The organic compound with higher molecular weight has higher removal affinity in coagulation process.Floc size and settling velocity of floc and sludge production all increased with the increase in NOM concentration. From the results of Capillary Suction Time (CST) tests, the floc formed with lower TOC readily released the water to make the dewatering process easier.The organic removal efficiency was significantly different for natural water containing non-homogeneous organic compounds compared to the synthetic water containing humic acid only (homogeneous organic matter). For example, the NOM removal efficiency was 80% for the synthetic water containing humic acid with TOC of 7 mgl-1 at pH 7; but the NOM removal for the pretreated pond water was 60%.

Removal of natural organic matter (NOM) using different coagulants and lightweight expanded clay aggregate filters

Chitosan and lightweight expanded clay aggregates were investigated as alternatives to traditional metal coagulants and anthracite in pilot scale coagulation-filtration experiments for the removal of natural organic matter (NOM) from drinking water. The raw water tested covered a range of colour and organic carbon of 15–50 mg Pt/L and 2–5 mg NPOC, respectively. Aluminium sulphate, poly aluminium chlorides with different calcium content, iron chloride sulphate, and chitosan coagulants were tested. The dual media filter bed was built with 0.6 m of 0.8–1.6 mm lightweight expanded clay aggregates (Filtralite) above 0.35 m of 0.4–0.8 mm sand. A conventional anthracite-sand filter with the same layer depths and grain sizes was used as a reference. In general, the maximum permissible concentration level of 0.1-mg Me/L controlled the minimum coagulant dose requirements when metal-based coagulants were used (Norwegian water quality standard). Typical NOM removal efficiencies obtained with metal coagulantswere in the range of 75–90% and 40–70% with respect to colour and organic carbon, respectively. Chitosan was able to remove colour quite effectively, but this coagulant was less effective with respect to organic carbon removal. Lightweight expanded clay aggregate was a good alternative to anthracite, with lower rates of head loss build-up, and increased filter run length and filter storage capacity. Only small differences in effluent water quality were detected with the two filters.

Coagulation-Direct Filtration of Soft, Low Alkalinity Humic Waters

Optimisation of coagulation-direct filtration processes with respect to efficient removal of humic substances, i.e. natural organic matter (NOM) has gained a lot of focus in many countries over the last years. This paper presents experimental results from pilot scale research studies aimed at optimising the coagulation-direct filtration process applied to soft and humic raw waters with low turbidity and alkalinity levels. Comprehensive tests of 3 types of raw waters with different NOM content, 5 types of coagulants, and 3 calcium sources for the purpose of corrosion control have been conducted. Removal efficiencies with respect to relevant water quality parameters are presented, with typical relationships between raw water NOM content, coagulant dose requirements and pH. Generally, when applying metal-based coagulants, residual metal concentration was the critical parameter regarding minimum coagulant dose requirements. Typical NOM removal efficiencies were in the range of 75-90% and 40-70% with respect to colour and organic carbon, respectively. Optimum pH conditions for the removal of NOM and/or residual metals do not always coincide with that of turbidity. The experiments also showed that poly-aluminium and ferric chlorides might have some benefits over alum in terms of dose requirements and range of optimum pH values, and that chitosan may be used for colour removal with good results.

Coagulation-direct filtration of soft, low alkalinity humic waters

Optimisation of coagulation-direct filtration processes with respect to efficient removal of humic substances, i.e. natural organic matter (NOM) has gained a lot of focus in many countries over the last years. This paper presents experimental results from pilot scale research studies aimed at optimising the coagulation-direct filtration process applied to soft and humic raw waters with low turbidity and alkalinity levels. Comprehensive tests of 3 types of raw waters with different NOM content, 5 types of coagulants, and 3 calcium sources for the purpose of corrosion control have been conducted. Removal efficiencies with respect to relevant water quality parameters are presented, with typical relationships between raw water NOM content, coagulant dose requirements and pH. Generally, when applying metal-based coagulants, residual metal concentration was the critical parameter regarding minimum coagulant dose requirements. Typical NOM removal efficiencies were in the range of 75-90% and 40-70% with respect to colour and organic carbon, respectively. Optimum pH conditions for the removal of NOM and/or residual metals do not always coincide with that of turbidity. The experiments also showed that poly-aluminium and ferric chlorides might have some benefits over alum in terms of dose requirements and range of optimum pH values, and that chitosan may be used for colour removal with good results.

Iron oxide adsorption and UF to remove NOM and control fouling

Addition of iron oxide particles to a UF system can significantly increase NOM removal efficiency, slowing membrane fouling.This study applied a novel single‐fiber membrane module to study fouling of ultrafiltration (UF) membranes by natural organic matter (NOM) molecules, and used a combined iron oxide–UF process to reduce that fouling. Addition of iron oxide particles to a UF system can significantly increase NOM removal efficiency, because NOM molecules that would otherwise pass through the membrane sorb to the oxides and are retained. Furthermore, despite the fact that iron oxide particles cannot selectively adsorb foulant molecules, their presence in the system can reduce the membrane fouling dramatically. This effect is mediated through two processes: a decrease in the NOM concentration in the circulation loop because of sorption and the formation of iron oxide cake layer deposits on the membrane surface. In such a system, the condensed layer of NOM forms on top of the cake, protecting the underlying membrane surface.