Impact of Micronutrient Technique (MNT) for biosolids reduction in wastewater treatment plants (original) (raw)
2022, HKIE Transactions
Over the last two decades, the wastewater treatment industry has faced a recurring issue: an overwhelming amount of biosolid (sludge) yield, high power consumption and foul odour due to its anoxic treatment procedures. Engineers in China and Canada have experimented with a different approach, using facultative anaerobic digestion, called the Micronutrient Technique (MNT). This biochemical technique mixes essential growth elements, namely amino acids, vitamins, purine, pyrimidine and minerals, to create MNT mixtures for the WWTP industries. The specific MNT mixture is based on gas detection on-site, the principle of bacterial anoxic reaction. Dosage with MNT has enhanced bioremediation and degradation of pollutants. In the experiment and case studies, it was found that in typical city and some industrial WWTPs, MNT offered a low-cost alternative with encouraging sludge yield and odour control.
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The co-digestion of biosolids and organic fraction of municipal solid waste was compared with the direct digestion of biosolids. Addition of organic fraction of municipal solid waste improved carbon-to-nitrogen (C/N) ratio from 8.10 to 17.68 or 20.55 in the feedstock, and led to a higher volatile fatty acid (VFA) concentration of about 1500 mg/L in the solution and a lower solution pH under 6 in the beginning 20-day during digestion. Although the total biogas yield increased by the mixed feedstock, the biogas yield peak was postponed for about 10 days and the maximum biogas yield rate was reduced. After digestion, over 30% of total solid (TS) and over 65% of volatile solid (VS) were removed. However, the COD concentration in the effluent was still higher than 2300 mg/L and needed further treatment before discharge. Because the production of municipal solid waste (MSW) and biosolids from municipal wastewater treatment plant (WWTP) continues to grow, the interest in alternative MSW and bio-solids management strategies intensifies, while the disposal capacity via traditional landfilling and incineration is diminishing [1,2]. Anaerobic biological treatment of organic fraction of MSW (OFMSW) and biosolids is an acceptable alternative because it not only reduces the volume of MSW and biosolids, stabilizes MSW and biosolids, but also recovers energy from MSW and biosolids in the form of methane, and produces a residue that can be used for soil conditioning [3]. But the implementation of anaerobic biological treatment of MSW at the full-scale level has been limited because of the relatively high cost and some technical problems. The anaerobic digestion of organic matter entails the conversion of dissolved and particulate organic matter into methane and carbon dioxide via a series of interrelated microbial metabolisms. Because of many complex interactions between various constituent populations of the microbial consortium, a number of factors can upset the anaerobic digestion process, for example, the methanogenesis inhibition by excessive volatile fatty acids (VFA) accumulation and the inhibition of propionate-and butyrate-degrading acetogens by high hydrogen levels [4,5]. Anaerobic digestion of biosolids and anaerobic digestion of MSW have been both investigated by researchers [6]. Digestion of nutrient-deficient MSW and biosolids can be improved through mixing each other [7–11]. Paper materials in MSW, such as office paper and newspaper, have a carbon-to-nitrogen (C/N) ratio ranging from 173:1 to greater than 1000:1, and sewage sludge has a C/N ratio varying from 6:1 to 16:1 [3], while the suggested optimum C/N ratio for anaerobic digestion is in the range of 20:1 to 30:1 [12]. Therefore, the mixing of biosolids and MSW can provide suitable nutrients for the digestion. In this study, biosolids and OFMSW from kitchen, vegetable market and yard were used as the feedstock in the co-digestion system. Experiments were carried out in the sequencing
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