Water reuse of sewage water by decentral waste water treatment combining SBR and membrane process using innovative ceramic flat membranes

 

 

To overcome material problems for water reuse applications ceramic membranes in a flat geometry have been developed and investigated. Results in table 1 show that the effluent water treated corresponds to EU bathing water guidelines. They don't have to be changed every year and have a long operation time between two cleanings.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These membranes can be used in larger centralized plants and in dezentralized applications for single houses avoiding channels, pipes, pump stations. Therefore the total system investment costs will be much lower.  Nevertheless the reuse-water free of bacteria, germs  can be used for applications like toilet flushing, laundry, gardening, machinery cleaning.

 

 

 

 

2. Requirements for water reuse

 

 

 

 

 

 

 

 

 

 

To avoid potential health desease coming from a exposition by reused water the usage as drinking-, body wash- and shower water cannot be generally permitted without having a double barrier system.

3. Conceptual design of water reuse plants

Two types of technology do exist: MBR plants as centralised large plants and small plants for decentralised system.

 

 

 

 

 

 

 

 

 

 

4. Examples for MBR water reuse plants

 

 

 

 

 

 

 

 

 

 

 

The main advantages of this example and generally mbr- plants are the elimination of bacteria by the mbr process resulting in a superior water quality suited for reuse, smaller sizes of the whole treatment line for installation in a house, enhanced elimination of pharmaceuticals, better process safety by safe sedimentation of sludge. The resulting disadvantages are the needs of better pre-treatment, mainly for organic membranes to minimise fouling potential, the higher process sensitivity related to changes in throughput and chemicals, scaling potential by hardness, higher energy consumption. But this energy consumption is comparable to aeration with N-elimination (20-30 kWh/PE*y).

 

 

 

 

 

 

 

5. Conceptual design for a basement located plant in a tower

 

 

 

 

 

 

 

 

 

 

In order to enhance the water reuse applications we calculated the process design for a 1.200 m³/d sewage water treatment plant (STP) located in the basement of a tower. The conditions are as follows: water flows by gravity into STP, space restriction require a compact plant design, quality suited for toilet flushing, cooling water make up, landscape and marine disposal.

 

 

 

This data correspond to about 4000 PEs each 300 L/day.

 

 

 

 

 

 

 

The calculations gave a peak flux of 100 m3/h, peakfactor is 12 hrs. Designing a sludge con­cen­tration of 15 kg/m³ -which corresponds to a lower plant design by a factor of 3 compared to con­ventional plants- we calculated the needs for the aeration basins to such a size that the technology can be inte­grated in the basement of a tower. The total calculations showed that the investment costs of such basement located plants (BLP) have a return of investment (ROI) of about 8 years based on local VAE water prices. This means that these BLPs can be operated with a profit rate of about 10 %/y, thus giving water for flushing toilets, for gardening, make up of cooling water.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6. Conclusions

 

 

 

 

 

 

 

 

 

 

It was discussed that the more than 100 years old centralised systems as installed in Europe cannot be transfered in threshold and development countries due to their

highly expensive needs for enhanced collecting systems with their leakages combined with not efficient enough elimination rates mainly to pharmaceuticals. Therefore other systems have to be designed using decentralized solutions without large collecting systems and leading to a superior water quality as Membrane Bioreactor Systems combined with conventional SBR systems. Installing the old plant concepts in threshold and development countries, where more than 2 million children each year die for want of a glass of clean water due to waterborne diseases, result in expensive and more than 100 years old technology, where cross contaminations to ground waters of disease sources like bacteria and germs cannot be avoided. To meet the millennium goals of UN each day 200.00 -300.00 peoples have to be supplied with technology for water treatment worldwide. This cannot be done really. Therefore new concepts have to be developed: better and cheaper. We think as a starting point 1. new concepts must be used wherever they will be cheaper, and 2. an optimisation between the mixture of centralised plant avoiding large channels, decentralised systems for single houses or towers has to be done before decisions will be done. 3. To meet the millennium goals for water quality the MBR technology has to be enhanced using such concept. All conventional technology like SBR and others can be combined with membrane technology where water reuse is evident to save water, where regional conditions require enhanced effluent parameters.