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Team:UniSalento Lecce/Applications
From 2013.igem.org
Applications
Purification plants implementation of heavy-metal removing bacteria
Our project aims to implement the bacterial heavy metal storage system in a common water purification plant. There are two phases in which such a system could be integrated : the first sedimentation step and the oxidative phase of the polluted water purification process.
A typical water treatment plant consists of:
- Screening
- Grit removal - oil extraction
- Primary sedimentation
- Oxidizer tank
- Secondary sedimentation
- Disinfection
It is possible to integrate the bacterical system in the sedimentation tank, with the periodic removal of the superficial layers of filter sand, to remove also the bacterical component that constitutes the active bio-film to eliminate the pollutants retained by the microorganisms themselves. The flow of water must undergo three additional purification steps downstream, ensuring greater safety and further effectiveness in removing pollutants.
The second possibility is to integrate the system with populations of microrganisms that compose the active sludge in the oxidizer. This has the advantage of leveraging the existing sludge elimination systems to also remove bacteria, which have accumulated heavy metals from treated solution. Some operating problems may arise due to competition between the various living components of the activated sludge system. It should also be considered the environmental component like the strong stress due to variations in temperature and volume of water to be purified (that depends on the rainfall) which may, as in every living system, lead to changes in the rates of growth and efficiency of in vivo operation of the protein-dependent metal storage system
Sedimentation tank
One of the main elements constituting the biological treatment plant is the sedimentation tank.
The sedimentators must be dimensioned taking into account water infiltration which increases the overall magnitude , that varies considerably in the course of the seasons. Particularly important is the influence of flow rate on separation efficiency of sedimentation tanks: due to a reduction in the efficiency you have an excess of solids that passes from the primary sedimentation to oxidation and a loss of biological mass from the secondary sedimentation, with an increase of suspended solids and to a decrease of the efficiency of removal of soluble pollutants that involves a worsening of the quality of the effluent solution.
It is therefore necessary to provide for install the floodways full, that allow the smooth operation of the equipment , within the limits of oversizing adopted in the design phase.
The oxidation of compounds in solution, operated by various types of microorganisms, starts already in these tanks ensured by agitation produced by mechanical stirrers (in figure: vertical axis turbines agitators).
The following passage through the oxidizer tanks involves the degradation of most of the substances present in the polluted solution. The process requires the work of the biological component of the system, in fact, in these tanks is present the so-called activated sludge. Nevertheless, already in the sedimentation tanks, on the top of the filtration sand, will tend to form a thick biologically active mud layer, that will have to be scraped off every now and then.
Activated sludge (oxidizer tank)
The most used activated sludge systems are called sequencing batch reactors (SRBs), term that best expresses its way of operative regime. The SRB reactors operate in cycles (usually one or more cycles per day). Each cycle consists of steps that occur in discrete periods of time. The steps are:
- Filling
The slurry is pumped into the reactor (aeration tank). The filling period can be static, mixed (activated sludge sediment is mixed in anoxic or anaerobic conditions with the sewage influential) or aerated. - Reaction
During this period, are completed the reactions started during the filling period. The reaction period can be divided into sub-periods anoxic, anaerobic and aerobic. - Sedimentation
One of the main advantages of the SBRs is that the separation of the active mud takes place in the whole volume of the reactor in state of quiescence. - Decanting
The treated slurry is separated from the activated sludge and unloaded from the reactor. - Rest
It's the period between the filling and decanting, is sometimes used in case of multi-reactors. The excess activated sludge can be eliminated in this period.
In all activated sludge plants, once the wastewater has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the treated supernatant is run off to undergo further treatment before discharge. Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new wastewater entering the tank (return activated sludge R.A.S.). Excess sludge (surplus activated sludge S.A.S. or waste activated sludge W.A.S) is removed from the treatment process to keep the ratio of biomass to food supplied in the wastewater in balance, and is further treated by digestion, either under anaerobic or aerobic conditions prior to disposal.
At the last phase, after the secondary sedimentation, the purification process terminate with the disinfection in wich the water is disinfected with chlorine in order to kill pathogens and prevent regrowth in the distribution system. From here it goes to the distribution system.
Polluted water biological treatment plant
The treatment plants are located at the end of industrial effluent or sewer networks, which may be of two types :
- separate and distinct systems of pipes, for sewage and stormwater
- a network unit made with a unique system in which everything flows
The flow of slurry varies during the day as a function of the rhythms of activity of the population served; these variations affect both the dimensioning of the systems, since the individual treatment units must ensure a sufficient retention time even at higher flow rates , both on the operation, as it must be taken appropriate precautions to always get the best treatment efficiency. Changes in the scope must also be taken into account for the sampling operations, which must be representative of the real conditions.
The depuration plant
In the design of a water treatment plant, particular importance is the hydraulic profile, that is the succession of the levels of constituent units the plant itself, which must be calculated in such a way that:
- the hydraulic gradient , in partial sections and in that overall , must to be appropriate to allow the passage of slurry through the system even at maximum flow of the sewerage or of the receiving body
- the altitude, at which should be initially led the sewage with lifting stations, must be defined
The hydraulic profile is generally calculated to achieve the flow with minimum energy consumption for lifting may be required.
We thank Dr. Eng. Antonio Leanza for helping us in modeling in CatiA V5 the purification plant and for his ideas on technical applications.
References
- Roberto Passino, Manuale di conduzione degli impianti di depurazione delle acque, 1999, Zanichelli/ESAC
- D. Suresh Kumar and Dr. V. Sekaran, FBBR and MBBR Bioreactors for Sewage Treatment, International Journal of Environmental Engineering and Management ISSN 2231-1319 Volume 4, Number 1 (2013), pp. 73-88© Research India Publications
Probiotics to sequester the nickel excess in the intestine
Nickel is a heavy metal, known today primarily as a pollutant. But naturally, this substance also has a role in biological systems, where it is present in very small quantities: the biological function of nickel is involved in hormonal metabolism, in maintaining the integrity of cell membranes, as a component of certain enzymes (arginase, trypsin, carboxylases), in the metabolism of glucose and lipids and in the stabilization of nucleic acids. In recent decades, nickel has become famous for the increase in individuals allergic to this chemical element: Italy is the first country in Europe to the prevalence of individuals allergic to nickel, equal to about 32%. How does it manifest this allergy? According to two forms: allergic contact dermatitis (mainly when the metal comes in contact with skin and mucous membranes) and systemic nickel allergy syndrome SNAS (mainly when the metal enters the human body through food). Food usually contains a few micrograms of nickel, but with the pollution of land can contain up to hundreds (cereals and legumes are among the foods richest in nickel). Since the absorption of nickel takes place for the most part in the intestine, and knowing the efficient homeostasis of nickel in Helicobacter pylori, our team thought it would be useful to engineer some species of bacteria commonly used as probiotics with the protein HPN, which has the characteristic to bind the nickel with high affinity, removing it from the bowel. The idea is to use gram-negative species harmless to human health, such as Bacillus or Lactobacillus: the former tend to form spores in their life cycle, so they may easily exceed the gastric barrier and germinate in the gut, going to compete with the resident flora, and the latter are normal constituents of enzymes present in milk, yogurt and other dairy foods. In particular, just turning Lactobacilli with Hpn you could create a yogurt or milk suitable for people allergic to nickel, which for them would be not only a safe food but also a real drug. Then these microorganisms accumulate the metal at cytosolic level means Bioconcentration: not arise the problem of disposing of bacterial biomass, because bacteria, that sequestered the metal, would normally be expelled via the fecal-oral circuit.
