- Nitrification - biological oxidation of ammonium (NH4-N) to nitrite (NO2) and nitrate (NO3) in aerobic wastewater systems. This is a two step process usually accomplished by Nitrosomonas & Nitrobacter sp.
- Denitrification - is the reduction (or use of the bound oxygen by microbes) which converts NO3 or NO2 into N2 gas. Denitrification occurs under anoxic conditions in the presence of soluble organics. Many bacteria can convert NO3 with fewer using NO2 as an alternative electron acceptor. Nitrate/Nitrite are preferentially used as an alternative electron acceptor (O2 source) over SO4, Fe, CO2
- AOB - ammonia oxidizing bacteria (ie Nitrosomonas & Nitrobacter)
- AnAOB or Anammox - organisms that take nitrite (NO2) + ammonium (NH4) and convert it directly to nitrogen (N2) gas. Requires a long sludge age (slow reproduction by these organisms) and proper anoxic conditions for the "shunt" to occur
Today, I wanted to cover a few definitions that can cause some confusion during conversations between operators.
"If you can't describe what you're doing as a process, you don't know what you're doing."
W. Edwards Demming
Demming's statement on quality control in manufacturing also holds for wastewater monitoring. Often we run tests such as SV30, clarifier bed depth, oxygen uptake rates, and microscopic exam but do it just to record data and do not link it into a controlled process of treating wastewater.
Each control test is linked to effluent quality, but because biological wastewater treatment is dealing with living organisms can have more variation and conflicting (at least on the surface) results.
For example, the normal first indication of a toxic shock to the system is an increase in effluent turbidity and deflocculation causing solids carryover in the secondary clarifier. If operating one of the newer membrane systems (MBR), you don't get this key indicator of effluent TSS carryover. So what should operators do to close this gap in information? In the case of MBR systems, operators should pay closer attention to turbidity in the SV30 supernatant and combined with a more through exam of the bacterial floc - with special attention paid to free bacteria and floc density. This means that we look beyond counting protozoa or metazoa and develop a process for looking at the floc on a daily basis.
Each system has some variation from the ideal wastewater unit used in training and engineering manuals. For operations, we need break treatment down according to simple monitoring tests that can be related by correlation or regression analysis to effluent quality. The ideal is too have a model that can predict effluent quality by daily tests done in the unit. We know BOD is not going to be in the model, so we often substitute COD, TOC or filtered TOC.
While I went through this topic quickly in this post, I am going to break out more information on each test and how what is observed can relate to microbial health over the next several posts. With tools to related test results to microbial health, you can construct the model that predicts your effluent quality.
In Houston, summer temperatures are just around the corner and collection system water temperatures will be consistently above 20oC where sulfate reducing bacteria (SRB) will flourish in anaerobic sections of the collection system. The following shows the steps in sulfide formation and natural sulifde oxidation can further corrode concrete and metals by forming sulfuric acid.
Molecular Screening for Enhanced Biological Phosphate Removal Organisms (EBPR) - getting a better grasp on a poorly understood group of microbes.
EBPR (Enhanced Biological Phosphate Removal) is a key part of phosphorus removal strategy along with tertiary coagulant/polymer treatment in final clarification. While we tend to discuss using either a biological phosphate removal or chemical precipitation approach, combining both technologies can improve effluent quality and save on costs as we don’t push either technology to its practical limits.
In both chemical and biological phosphate removal, we are fixing soluble phosphate into the floc and removing the floc from the water column. While many bacteria naturally store some phosphate, we are looking to provide conditions that promote the growth of bacteria that are “super phosphate” accumulators during aerobic growth. These bacteria store approximately 6x the phosphate of other wastewater bacteria inside their cells. We know cycling between anaerobic with soluble organics at the influent followed by aerobic oxidation sections promotes growth by taking advantage of the phosphate accumulator’s unique ecological niche. However, we don’t know much about the actual organisms.
The best organisms for EBPR are not cultured using standard microbiology techniques like a majority of bacteria present in nature. We tended to call many of these EBPR organisms “Candidatus acccumulibacter” – but we did not know much about them.
Using modern high throughput DNA based technologies including 16S and qPCR techniques, we are finally getting an idea to the actual organisms and their diversity in organisms best suited for EBPR. However, this process involves a learning curve. Key to discovering these organisms is finding a polyphosphate kinase (PPK1) gene to differentiate inside the group. But this is not the end to the research. Using 16S testing a group of researchers found 10 clades of EBPR organisms. Using the newer PPK1 qPCR on the 10 clades only covered 50% of the 16S identified group. So, the diversity is very high inside the EBPR group.
So what does this mean for wastewater engineers and operators? As we develop more molecular tools to isolate and determine which EBPR organisms are present, we can find ways to optimize the EBPR process by tracking DNA drift in response to operational changes or variation in influent makeup. This technology is in its infancy with respect to EBPR microbes, but will be a key part of lowering phosphate removal costs from wastewater.
Over the past few days, I have read several articles on a massive fish kill that left 35 tons of dead fish in lake in Hainan China. Unlike a fish kill from a major dock/warehouse fire last year where cyanide and other compounds got into the water, the cause of this fish kill is not as obvious. Early speculation blames an increased salinity in the water. While some may think of this as natural, there is potential for industrial runoff, diversion of fresh water flows and other human activities to change the salinity in a lake.
Key is that an indicator species, fish, have been killed by some agent. Also, the amount of fish (35 tons) represents a huge pollution load that can further degrade the lake's ecosystem.
Here is a link to an article with pictures.
In many areas of the world, people live "off-the-grid" with respect to not having access to the sophisticated collection systems and a centralized sewer treatment plant. Without a treatment system, their untreated wastewater from households and farms ends up in waterways and even groundwater. This is major concern as enteric bacteria and other pollutants can ruin the water supply for drinking and fishing purposes. So what is the best way to treat this waste?
I am inclined to recommend construction of a simple anaerobic digester design that would also provide beneficial methane for cooking. The simplest system uses recycled plastic drums. Household waste is added via an inlet pipe and the drum is kept tightly sealed. Off gas is collected in a second drum or inflatable rubber bladder for use as fuel source (reduces need for firewood). A port for liquid discharge is also needed on the digester. The waste is only partially treated and should be land applied as fertilizer or treated in an oxidation pond to reduce ammonia and fecal counts before discharging into a river. A quick internet search gives plans for numerous digester plans an schematics.
By giving residents in developing areas simple recycled supplies and plans, they can get the benefits of waste treatment and obtain fuel for cooking. Numerous NGOs are helping to spread this technology and the benefits of operating a small anaerobic digester for households and farms.
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