The Microvi MNEffect: 1. Resource Recovery and the Drive Towards a Circular Economy

 The Microvi MNE? (MicroNiche Engineering) process is highly effective at removing soluble components from wastewater (and water) such as ammonia and carbon. In order to meet effluent standards, wastewater treatment requires the removal of both particulate and soluble matter. Instead of just removing particulate matter, why not use it for the production of valuable products? Shifting our view of wastewater treatment facilities to resource factories, Microvi MNE is an ideal solution. Because Microvi’s treatment technology has virtually zero biological solids production, its process is perfect for modern day resource recovery and the drive towards a circular economy.

Historically a conventional wastewater treatment process consisted of some form of headworks to remove gross solids and heavy particles such as grit, followed by primary settlement to remove particulate matter over a certain particle size.  The discharge is fed to a biological process where the remaining organic material is converted by biological activity.

The performance of the primary tanks is highly dependent upon a number of factors, but typically for conventional primary settlement we expect 50 – 70% Total Suspended Solids (TSS) and 20 – 40% of Total Biological Oxygen Demand (TBOD) removal.

We rely on biological processes to capture the remaining suspended solids and convert particulate and soluble BOD into cell mass and carbon dioxide. This generated cell mass is then separated from the treated water through physical means (usually gravity, but occasionally barrier methods such as membranes or filter media). Whether you are using a suspended growth or fixed film treatment process, this mechanism removes particulate BOD from wastewater to relatively low levels.

Shifting our view of wastewater facilities to resource factories, we are more interested in retaining as much of the native particulate BOD and passing it through for value recovery—usually anaerobic digestion for the generation of biogas (methane and carbon dioxide). Primary solids are easier to digest and produce higher specific gas yields over secondary solids.   The higher the ratio of primary to secondary, the lower the net cost of solids treatment and disposal, especially when considering the costs of thickening and dewatering chemicals.

It is virtually impossible to avoid particulate capture and treatment within a conventional biological process. Under high rate conditions, particulate BOD is captured but not fully hydrolysed. The resulting solids mass remains highly active leading to serious issues such as high hydrogen sulphide (H2S) levels in downstream storage tanks and must be handled carefully and quickly.   I’ve experienced first-hand a biological process designed for “soluble-only” BOD removal resulting in incredibly poor performance. It generated unprecedented hydrogen sulphide within the secondary and thickening process with over 500ppm of H2S in the pre-thickened sludge storage tank headspace, and in the thickening building itself.

High TSS removal using chemically assisted settlement can deliver close to 95% solids removal. If coupled with two stage removal making use of new technologies such as cloth-pile filters or high efficiency dissolved air flotation (DAF), reliable single digit TSS numbers may be achievable. The use of chemicals may be considered cost prohibitive. However, where chemical phosphorus removal is used in the primary stage, there is no additional cost for achieving these low TSS levels.

Applying a biological process downstream of enhanced primary would remove the soluble BOD and ammonia, however this would still lead to the production of cell mass requiring a downstream solids removal process. The virtually non-existent particulate mass in the influent also has some impact on gravity solids separation, reducing the stability of suspended growth systems and the settle-ability of fixed film systems. 

Microvi MNE can be designed to only remove soluble components, allowing particulate matter to pass through the reactor.  In effect, TSS in = TSS out, with only a very small increase due to indigenous growth.  Microvi MNE also provides an alternative to undertaking removal upstream of particulate BOD, giving the option for chemical phosphorus removal downstream using a high efficiency solids removal process, such as ballasted flocculation. This is especially pertinent for very low phosphorus levels where low TSS levels are required.

Though pass-through of particulate biodegradable matter is often considered a negative, it can be quite the reverse. The Microvi MNE process is poised to support the delivery of future treatment demands, including the drive towards a circular economy.

Microvi MNE has commercial installations in the United States and Australia and is being demonstrated at numerous wastewater treatment plants globally.  Microvi, along with our North American partner WesTech Engineering, Inc., and global partners in the UK and the Asia Pacific, are testing Microvi MNE as a resource recovery process.

You can learn more about Microvi MNE and our ongoing projects on our website at www.microvi.com.