| Bhushan Zarapkar |
Many waste water processing units use spiral wound membrane-based RO systems for recycle of treated effluent. The RO treatment process produces a small, but two to three times more concentrated reject stream (approximately 20-30 per cent of the treated water volume). For plants which are zero liquid discharge (ZLD) this reject needs further treatment. Usually this stream is sent for further volume reduction using evaporators like MEE (multiple effect evaporator) or MVR (mechanical vapour recompression) followed by spray dryers or solar ponds. All these post RO processes are energy intensive depending on fuel costs. The operating costs should be anywhere between Rs 300 to Rs 600 per 1000 litres of effluent.
| Typical membrane-based RO systems |
| Dr Jaideep Dudhbhate |
Is there a better solution? We believe there is. ATE offers ‘VSEP’ (Vibratory Shear Enhanced Processing), a patented membrane- based patented technology from New Logic Research Inc, USA to the Indian market. The final treated effluent (and RO reject) volume going to the evaporator (MEE /MVR) may be further reduced by about 30 per cent to 70 per cent, thereby reducing the cost of evaporation both in terms of Capex and Opex. VSEP has also been used as a single stage unit so as to eliminate the high cost of three stages of RO while obtaining the same efficiency. The VSEP system also generates permeate of a quality suitable for recycling.
| Typical membrane system RO system along with VSEP |
In the VSEP process, a shear is introduced at the membrane surface whereby the separation through membrane becomes very effective without any fouling at the membrane surface. This results in several advantages of VSEP over any conventional membrane-based filtration system.
- It is fouling resistant.
- Virtually no pretreatment necessary (in comparison to conventional systems)
- Low chemical consumption.
- Low reject volume going to MEE, thus reducing capital cost for a new MEE
- Higher recovery resulting in more volume being recycled. This results in reducing the requirement of raw water.
- Low foot print.
- Fully automatic with minimum manual intervention.
- Facility of remote monitoring.
- No foundation required.
VSEP finds application in difficult to handle waste streams from textile, pharmaceutical, chemical, distillery, dairy, food processing, electronics, pulp and paper, dyes and other manufacturing units.
| Sr. No. | VSEP specification | |
| 1.0 | Parameters | |
| 1.1 | Application | Reduction of feed volume going to evaporator |
| 1.2 | Design feed flow rate | 600 m3/day (Of RO reject feed) |
| 1.3 | % Recovery (40%) | 240 m3/day |
| 2.0 | Present feed quality | Present feed quality |
| 2.1 | Feed water quality. | COD: 1000 ppm TDS: 17000 to 20000 ppm |
| 3.0 | Pre-treatment | |
| 3.1 | Pre treatment | Only Micro screen 100 micron |
| 4.0 | Plant operation and maintenance | Plant operation and maintenance |
| 4.1 | Plant operation | Fully automatic |
| 4.2 | Pressure | 32 bar |
| 4.3 | Cartridge filter replacement | Not applicable |
| 5.6 | Membrane replacement | Expected once in two years |
| 5.0 | Cleaning in place (CIP) | |
| 5.1 | Frequency of cleaning | 48-72 hours and requires max two hours. |
Application Note:
The following application note will elaborate on the EVR application of VSEP in effluent treatment processes.
Objective of going in for VSEP: The objective was to reduce the volume sent for evaporation in a ZLD system so that the total cost of ownership of the evaporation system is reduced drastically.
Following are the major advantages seen with the use of a VSEP system for EVR.
- Virtually no pre-treatment and low chemical consumption during CIP.
- Low reject volume going to MEE, This has helped in drastically reducing the total costs of evaporation. This resulted in a very attractive payback of less than two years for EVR.
| Typical VSEP-EVR installations- | |
VSEP payback viz-a-viz MEE:
| Photograph of effluent samples from VSEP plant: |
Basis –
- Reduces volumetric load on MEE.
- Reduces volumetric load on MEE thus resulting in lowering of operating costs of MEE
Note: It can be seen that the reject from VSEP is highly concentrated.
| Approximate payback Calculations for VSEP | |||
| VSEP + MEE (50%) | MEE (100%) | ||
| 1 | Operating flow rate | 600 | 600 |
| 2 | Recovery VSEP | 40 | 0 |
| 3 | Recovery of secondary MEE | 95 | 95 |
| 4 | Approximate cost of VSEP units | 60000000 | 0 |
| 5 | Approximate cost of MEE | 7000000 | 15000000 |
| 6 | Total capex | 67000000 | 15000000 |
| 7 | Increase in capex due to incorporation of VSEP | 52000000 | |
| 8 | Steam consumption for MEE @ 0.34 ton steam/ m3 water evaporated | 116 | 194 |
| 9 | Power consumption of MEE @ 10 kW /m3 water evaporated | 3600 | 6000 |
| 10 | Operating cost on account of steam consumption of MEE (cost of steam Rs. 1200 / ton) | 139000 | 233000 |
| 11 | Operating cost on account of power consumption of MEE (cost of power Rs 6 / kWh | 21600 | 36000 |
| 12 | Operating cost of MEE (CIP, tube replacement etc. approx. Rs. 55 / m3 of water evaporated) | 19800 | 33000 |
| 13 | Approximate cost of operating VSEP including CIP, replacement cost of membrane, power etc. approx. Rs. 80 / m3 of water treated | 48000 | 0 |
| 14 | Operating cost of MEE / year | 6,58,46,000 | 11,02,30,000 |
| 15 | Operating cost of VSEP / year | 1,75,20,000 | 0 |
| 16 | Total operating cost | 8,33,66,000 | 11,02,30,000 |
| Saving in operating cost due to incorporation of VSEP | 2,68,64,000 | Simple payback period | |
| Simple payback period | 2.23 | 2.23 | |
Conclusions:
It is seen from the sample above that VSEP can easily help units which have a ZLD requirement with evaporation as final stage to save operational expenses drastically. Also it has several advantages over any conventional membrane-based filtration system.
- Very low pay back period making VSEP system very attractive as a part of ZLD system.
- Virtually no pretreatment necessary (in comparison to conventional systems)
- Low chemical consumption
- Low reject volume going to MEE, thus reducing capital cost for a new MEE
- Higher recovery resulting in more volume being recycled. This results in lowering requirement of raw water.