The MBR Book: Principles and Applications of Membrane

138 The MBR Book
For each of the trials operational problems were encountered which led to irreversible,
and sometimes irrecoverable, fouling. This included partial aerator blockage,
membrane tube blockage and partial dewatering (i.e. sludge thickening due to failure
of the feed flow). Repeated chemical cleans were thus employed over the course of the
trials, both for maintenance and recovery of membrane permeability, and relaxation
was only introduced mid-way through the trials. A strong temperature dependence of
permeability was noted for all membranes tested at low temperature, with the sustainable
permeability decreasing markedly at temperatures below 10°C.
It was concluded from this trial that the Kubota could not be operates routinely at net
fluxes of 38.5 LMH, although the fouling rate was decreased when relaxation was
introduced. Peak flux operation of both the Zenon and Kubota systems at 41–43 LMH
for 100 h led to a manageable decline in permeability, however, with permeability
recovering to normal levels on reverting to low flux operation. Under the most optimal
conditions of a regular maintenance clean and backflushing at 20.8 LMH, the
permeability of the Mitsubishi Rayon membrane was maintained at between 200
and 300 LMH/bar at some unspecified flux. A net flux of 20.8 LMH was achieved for
a period of 5 days, but peak fluxes of 28 LMH or more led to a rapid decline in permeability.
Enhanced cleaning at higher reagent concentrations (1 wt% NaOCl) and
temperatures (40°C) may have led to the noted deterioration of the membranes. The
Norit X-Flow membrane was apparently, eventually, successfully operated at 37 LMH
with weekly maintenance cleaning and night-time relaxation (4 h every 24 h). However,
there were problems maintaining this flux due to tube blockage. The Zenon
plant, fitted with the 500 c module, appears to have been operated under conditions
whereby a reasonable net flux of around 20 LMH with an accompanying permeability
of 200–250 LMH was sustained through maintenance cleaning twice weekly
over an extended time period. It is possible that the other technologies could have
also been sustained higher fluxes in operated under more optimal conditions.
3.2.3 Point Loma Wastewater Treatment Plant, San Diego
This trial resulted from an award made to the City of San Diego and Montgomery
Watson Harza (MWH) from the Bureau of Reclamation to evaluate MBR � reverse
osmosis (RO) technology for wastewater reclamation (Adham et al., 2004). A 16-month
study was conducted at the Point Loma Wastewater Treatment Plant (PLWTP) at
San Diego, CA on four MBR systems: Mitsubishi Rayon, Zenon, Kubota and Memcor.
The technologies were each challenged first with raw wastewater (Part 1) and then
with advanced primary treated effluent containing polymer and coagulant residual
(Part 2), arising from clarification with ferric chloride (27 mg/L, average dose) and a
long chain, high-molecular-weight anionic polymer. Details of feedwater quality
(Table 3.8), MBR technology design (Table 3.9) and operation (Table 3.10) are given
below.
In this trial only the advanced primary treated effluent feedwater was tested on all
four technologies. Results from untreated primary sewage were inconclusive since
the feed water evidently contained unclarified ferric coagulant. All four technologies
performed satisfactorily with respect to nitrification, disinfection and BOD removal.
Only the Kubota was operated with denitrification and consequently demanded less