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水处理英语论文:Membrane Bioreactors (MBR)

来源: 作者: 发布时间:2010-11-27  

Public concern over health and the environment, combined with increased requirements for municipalities to reuse wastewater, have created a need for new technologies that can generate high quality effluent at low cost.

Throughout the world, there are hundreds of Membrane Bioreactor (MBR) systems in operation with many more in the design/construction phase.  These range from small to large systems, treating both municipal and industrial wastewater.  Small MBR systems are often used for water reuse within commercial developments, such as office complexes or shopping malls, whereas municipalities and industries operate the larger plants. 

MBR technology has come a long way in a relatively short period of time.  For example, in 1996 ZENON Environmental Inc. was installing municipal ZeeWeedÒ MBR systems with average capacities of 0.2 MGD.  In 2003 - just eight years later – MBR plants with capacities > 10 MGD are being constructed by ZENON.

Why is this paradigm shift occurring?  Because MBR systems bring many specific benefits compared to conventional activated sludge and tertiary treatment systems.  The benefits discussed below are based on ZeeWeedÒ MBR technology and the use of reinforced hollow fiber ultrafiltration (UF) membranes (Figure 1).

 

Figure 1 – Comparison of MBR vs Conventional Technology

 

 

ZeeWeedÒ MBR

Conventional Tertiary Treatment

Clarifier

No

Yes

Filter

No

Yes

MLSS

> 10,000 mg/L

< 5,000 mg/L

SRT

10-365 days

< 20 days

Footprint

Typically 5-10 times smaller

-

Process Stability

Not susceptible to upsets

Susceptible to sludge bulking

 

The biggest benefit is that MBR systems produce consistent, better than tertiary quality effluent (Figure 2).  The UF membranes replace the primary and secondary clarifiers, providing solids separation by filtration instead of gravity settling.  In a conventional biological system, performance and efficiency is limited by the ability of the clarifier to settle the solids from the mixed liquor stream.  This is a function of the operators skill, sludge settleability, basic clarifier design, solids management and the external rate of variability in hydraulic or organic loading.  When upsets occur, solids can be lost and plant performance compromised. 

 Figure 2 – Typical ZeeWeedÒ MBR Effluent Quality

 

Parameter

Effluent Quality

BOD5

<2 mg/L

TSS

<2 mg/L

Ammonia

<1 mg/L

TN

<3 mg/L*

TP

<0.1 mg/L**

Turbidity

<0.1 NTU

SDI

<3

* with anoxic zone

** with coagulant addition

 

The advantage of using UF membranes:

1、   The effluent is suspended solids free, independent of the biotreatment efficiency.  The effluent is free of protozoa and cysts, and has significantly reduced bacteria and viral counts, providing an effluent that can also meet future more stringent regulations.

2、   A suspended solids free effluent ensures that insoluble phosphorus is retained within the bioreactor, further assuring a high quality effluent.  This also translates into lower coagulant dosages, since the requirement is only to micro-floc the phosphorus to be removed.  This allows for the development of plants faced with stringent phosphorus discharge requirements.

3、   The effluent levels of BOD, nitrogen, phosphorus and suspended solids are very low, meeting tertiary treatment criteria without the need of additional filters.

 

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