Improvement of municipal wastewater pretreatment by direct membrane filtration

Abstract

The high content of particulate matter in municipal wastewater hinders the conventional anaerobic treatments at psychrophilic temperatures. The hydrolysis of the particulate chemical oxygen demand (pCOD) could be the limiting step under these conditions. Therefore, new pretreatments or improved conventional pretreatments are needed in order to separate pCOD. In this work, direct membrane filtration of municipal wastewater, using an ultrafiltration membrane, was investigated. This intensive pretreatment, which aims to separate soluble chemical oxygen demand (sCOD) and to concentrate pCOD, together with anaerobic treatments of both streams at psychrophilic and mesophilic conditions respectively, could be an alternative to the conventional activated sludge process. The obtained results show a removal yield of 24.9% of the total solids (TS) and 45% of total chemical oxygen demand (tCOD), obtaining a permeate free of suspended solids. This physical removal implies the accumulation of solids inside the membrane tank, reaching the values of 45.4 and 4.4 g/L of TS in the sedimentation and filtration sections, respectively. The membrane operated with filtration, backwashing cycles and continuous gas sparging, with a permeate flux predominantly around 10 L/(m h). The results show the viability of the technology to concentrate pCOD and so to improve energy recovery from municipal wastewater.

Direct Membrane Filtration of Municipal Wastewater: Studying the Most Suitable Conditions for Minimizing Fouling Rate in Commercial Porous Membranes at Demonstration Scale

“…According to these results, organic matter seems to be the main fouling promotor during filtration for both membranes, showing a special relevance for the MF since it was operated during relatively short time periods (around 5–7 days) (see Figure 5 ). In this regard, other studies have also reported similar results when applying basic solutions for membrane cleaning [ 17 , 33 , 34 ], also concluding that organic matter was the major fouling promotor during direct MWW filtration. Nonetheless, inorganic fouling (mainly related to inorganic compound precipitation on the membrane) also had a significant effect on UF membrane filtration, which operated for a middle-term (around 1–2 months) (see Figure 3 ).…”

A Rotating Hollow Fiber Module for Fouling Control in Direct Membrane Filtration of Primary Settled Wastewater

“…(2017) evaluated the feasibility of direct membrane filtration process for the treatment of municipal wastewater. After more than one month of operation at sustainable conditions, these authors achieved a considerable irreversible fouling (68%), which can only be removed by chemical cleanings . Therefore, because of the expected high levels of irreversible fouling during long-term operation, enabling frequent chemical cleanings (i.e., chemical-enhanced backwashing) during the routine operation may be crucial for the further development of this technology.…”

Direct Membrane Filtration for Wastewater Treatment Using an Intermittent Rotating Hollow Fiber Module

“…By using a micro/ultrafiltration membrane, solids and pathogens can be removed from wastewater producing a readily reclaimed wastewater for irrigation and landscaping. In terms of chemical oxygen demand, removal efficiencies for municipal wastewaters in the range between 45% and 90% have been reported, according to membrane and wastewater characteristics [9][10][11]. Several advantages over other comparative technologies (e.g., activated sludge followed by micro/ultrafiltration or membrane bioreactor) have been described: lower energy consumption, smaller footprint and higher nutrient content of the reclaimed wastewater.…”

“…has been also reported for submerged hollow-fiber modules with gas sparging [9]. In addition, regular in situ chemical cleanings have to be adopted (every 6-48 h of filtration) for achieving a sustainable operation, in detriment of membrane lifespan.…”