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MICROBIAL BIODEGRADATION OF POLYETHYLENE
OF LOW DENSITY, UNDER CONTROLLED THERMAL
CONDITIONS IN AIR LIFT BIO-REACTOR
Alexandra Milagros Hermoza Rojas
University Cesar Vallejo, (Perú).
E-mail: alexandrah@gmail.com ORCID: https://orcid.org/0000-0001-7468-8969
Jorge Jave Nakayo
Universidad Nacional Mayor de San Marcos - UNMSM, Lima, (Perú).
E-mail: jorge.jave@unmsm.edu.pe ORCID: https://orcid.org/0000-0003-3536-881X
Jorge Luis López Bulnes
Universidad Nacional Mayor de San Marcos - UNMSM, Lima, (Perú).
E-mail: jlopezb@unmsm.edu.pe ORCID: https://orcid.org/0000-0002-9583-1143
Vicenta Irene Tafur Anzualdo
National University Federico Villarreal, (Perú).
E-mail: itafur@unfv.edu.pe ORCID: https://orcid.org/0000-0002-1888-7848
Recepción:
18/09/2020
Aceptación:
02/11/2020
Publicación:
13/11/2020
Citación sugerida Suggested citation
Hermoza, A. M., Jave, J., López, J. L., y Tafur, V. I. (2020). Microbial biodegradation of polyethylene of
low density, under controlled thermal conditions in air lift bio-reactor. 3C Tecnología. Glosas de innovación
aplicadas a la pyme. Edición Especial, Noviembre 2020, 179-189. https://doi.org/10.17993/3ctecno.2020.
specialissue6.179-189
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ABSTRACT
The present investigation seeks to identify new mechanisms that serve as tools for
the mitigation of plastic contamination through the biodegradation of low density
polyethylene using microorganisms of the species Pseudomona aeruginosa (bacteria) and
Aspergillus brazilensis (fungus) under controlled thermal conditions in an airlift bioreactor.
The methods used were 2 samples of low density polyethylene with concentrations of
50 mg/L and 2 samples of 100 mg/L deposited in an airlift bioreactor under controlled
thermal conditions with a duration of 7 days. As a result it was obtained that the species
Pseudomona aeruginosa (bacteria) reduced the low density polyethylene sample by 2% with
a concentration of 49 mg/L at a temperature of 21.8ºC with a pH of 6.5 and dissolved
oxygen (OD) of 6.8 mg/L, likewise the species Aspergillus brazilensis (fungus) reduced the
low density polyethylene sample by 7% reaching a concentration of 93 mg/L at 22.1ºC of
temperature, 7.14 of pH and 7.45 of dissolved oxygen (OD).
KEYWORDS
Air lift bioreactor, Biodegradation, Thermal conditions, Low density polyethylene (LDPE).
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1. INTRODUCTION
As we know, plastics are a big problem nowadays, since we live in a world where people do
not have an adequate environmental conscience, unfortunately this generates a very negative
impact to our planet. Plastics have a low economic value in the market and are the most
used, therefore, the amount of plastic waste increases. In addition, he tells us that “In 2010,
8.07% of plastic waste was generated in our country and in 2011 9.85%, this indicates that
every year there is an increase in plastic waste. Plastic bags (low-density polyethylene) take
150 years to degrade, which is why we have been looking for alternatives to reduce the life
span of plastic, such as incineration, which causes health problems because it generates the
famous greenhouse gases (GHGs), in addition to the release of dioxins and furans (POPs)
that are highly carcinogenic according to the World Health Organization (WHO) (Barlow
et al., 2019).
Plastic waste is a worldwide problem since people use the bags only once, throw them away
and buy others again without realizing it; this is how pollution begins, causing damage
mainly to marine ecosystems, since fauna often confuses them with food. A study conducted
for MINAM in June 2012 indicates that Peruvians generate approximately 23,260 tons of
solid waste, which gives us a per capita production of 800 grams (Córdova et al., 2020).
A study released in 2015 tells us that sea turtles have been ingesting 52% of garbage, with
plastic waste such as bags being the most common (Inforegion, 2015).
Finally, according to the Peruvian newspaper El Comercio (2018), 79% of plastic waste
globally is found in dumps or thrown on the roads; only 9% is recycled and 12% is
incinerated.
2. MATERIALS AND METHODS
2.1. PLACE OF STUDY AND SAMPLING
In this stage the place to work was selected and was an informal dump located in the town
center of Santa Clara in the district of Ate in Lima in April, which presented a large
amount of plastic in an apparent state of degradation (Catto et al., 2016).
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Figure 1. Map of sampling points
2.2. ELABORATION OF AIR LIFT BIOREACTORS
The bioreactors are made in the laboratory, they have a cylindrical glass culture chamber
of 100 mm diameter by 200 mm height with a small pipe to take the samples, a deector
tube or central distribution of 80 by 28 mm, a venting lter attached to a regulating valve
for air output, control valves for air input/output and air ow connectors attached to the
tank pumps; which are the main source of oxygen for the bioreactor (Paço et al., 2017). The
culture chamber and deector tube, the bioreactor accessories such as the top cover (airtight
lid), air inlet/outlet control valves and air ow connectors are sterilized by immersion in
70% medicinal alcohol for 15 minutes and rinsed with puried water.
2.3. SOWING OF MICROBIAL CULTURES
The microorganisms chosen for the biodegradation process were a bacterium (speudomona
aeruginosa) which was seeded on Trypticase Soy agar and incubated for 24 hours at a
temperature of 30oc to 35oc and a fungus (Aspergillus brasiliensis) grown on Saburo
Dextrose agar, incubated for 48 hours at a temperature of 20oc to 25oc (Giacomucci et al.,
2019).
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It should be considered that for the process to be more eective, the strains should be used
within the rst two hours after leaving the incubator.
2.4. BIOREACTOR OPERATION OF THE CULTURES
The microbial colonies kept inactive in refrigeration are reactivated in new plates with
half Trypticase Soy and Saburo Dextrose forming in seed inocula for the bioreactors. The
proportion is 15% of the total volume (1000ml). The operation starts with the ignition of
the air pumps, the total opening of the vent valve for a period of at least 7 days (Soto, 2016).
2.5. CONCENTRATION OF LOW DENSITY POLYETHYLENE BAGS
The degradation of the low density polyethylene (LDPE) is determined with the decrease
of concentrations placed in the bioreactor, for which we work with 50mg/L for the type A
bags, 100 mg/L for the type B bags, as concentrations for the beginning of operation, these
samples are measured again after three days. To nd the nal concentration, the whole
culture medium is autoclaved for 15 minutes, then the low density polyethylene (LDPE)
samples are extracted, rinsed with puried water and taken to the oven for 12 to 24 hours
at 80°c. Finally, the weighing is done in the analytical balance.
Table 1. Table of concentrations of low density polyethylene (LDPE) type A.
Bioreactors
Concentrations of LDPE type A (mg/L)
DAY 0
DAY 3
DAY 7
pseudomonas 1
50
49.000623
49
aspergillus 2
50
45.000023
45
2.6. DETERMINATION OF TEMPERATURE, DISSOLVED OXYGEN AND PH
The determination of the internal temperature was obtained at the beginning, after three
days and at the end after 7 days by means of a thermometer, for dissolved oxygen in the
same time interval it will be determined by an oximeter in the unit’s mg/L and nally
for the determination of the pH in the same time interval it was obtained by means of a
potentiometer (Janczak et al., 2019).
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2.7. STATISTICAL ANALYSIS
The statistical test Anova was used to compare the low density polyethylene (LDPE) groups
in a quantitative variable where p < α, p-value =0.04 to α =0.05, T for the samples in the
dierent groups, since the group of individuals sampled is less than 30.
2.8. RESULTS AND DISCUSSION
The results obtained in low density polyethylene (LDPE) type A using the concentration
of 50 mg/L in relation to the determination of concentrations had a decrease of 1%
for pseudomonas and 5% for aspergillus, taking into account the higher eciency of the
latter, according to the variation of the temperature of 1°c. inuenced in the eciency
due to the fact that these temperatures are within the environmental thermal conditions.
However, the concentrations of dissolved oxygen increased by 4% pseudomonas and 20%
for aspergillus during the days of experimentation, as opposed to a reduction of pH by 17%
for pseudomonas and 13% for aspergillus (Sadhukhan et al., 2019).
Table 2. Table of concentrations of PEBD type B.
Biorreactors
Concentrations of PEBD type B (mg/L)
DAY 0
DAY 3
DAY 7
pseudomonas 1
100
98.001246
98
aspergillus 1
100
93.000064
93
The results obtained in low density polyethylene (LDPE) type B using the concentration
of 100 mg/L in relation to the determination of concentrations had a decrease of 2%
for pseudomonas and 7% for aspergillus, taking into account the higher eciency of the
latter, according to the variation of the temperature of 1°c. inuenced in the eciency
due to the fact that these temperatures are within the environmental thermal conditions.
However, the concentrations of dissolved oxygen increased by 8% pseudomonas and 4%
for aspergillus during the days of experimentation, as opposed to a reduction of pH by 19%
for pseudomonas and 11% for aspergillus.
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3. DISCUSSION
Microorganisms are capable of biodegrading low density polyethylene (LDPE) under
certain controlled thermal conditions. On day zero, two samples of low density polyethylene
(type A) with concentrations of 50 mg/L and two samples with 100mg/L of low density
polyethylene with biodegradable additives (type B) were taken. On the last day of the
process, sample 1 of type A had a nal concentration of 49mg/L and sample 2 reached
a concentration of 45mg/L. The rst type B sample reached a concentration of 98mg/L
and the second one a concentration of 93mg/L, which was the sample where the highest
degradation was obtained with a temperature of 22.1ºc.
For an ecient degradation by microorganisms, a favorable thermal condition is needed.
Native bacteria present in worm, horse and chicken humus biodegraded polyethylene
terephthalate and oxo-polyethylene eciently at a temperature of 22ºc in 35 days. For this
research, an average temperature of 22.1ºc was obtained on the last day of the process, this
being the most ecient temperature for the biodegradation of low-density polyethylene
with Aspergillus brazilensis (Perpetuo et al., 2020).
The chemical conditions are important for microbial biodegradation, the pH of the samples
was determined during the process. The most ecient pH for the sample with Pseudomona
aeruginosa was 6.49 and for the sample with Aspergillus brazilensis was 7.14. This value was
the most ecient for the whole process. For the optimum pH for the polyethylene sample
with bacteria such as Pseudomonas sp was 5.5 and for the sample with fungi (unidentied
yeast) was 7 (Alvarado et al., 2020).
Finally, a percentage of 1% of degradation was obtained with Pseudomona aeruginosa for
sample 1 of polyethylene type A and for the degradation with Aspergillus brazilensis for
sample 2 of the same type of polyethylene a percentage of 5% was obtained. For sample 1
of polyethylene type B with Pseudomona aeruginosa a percentage of 2% was obtained and
for sample 2 of the same type of polyethylene with Aspergillus brazilensis a result of 7%
of degradation was obtained. For NOVOTNÝ, C (2015) in a period of six weeks and with
a temperature of 28ºc the samples of PETP/LA with Pseudomona aeruginosa had mass
reductions of up to 5-10%.
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4. CONCLUSIONS
Microbial biodegradation of low-density polyethylene was evaluated in Santa Clara in an
air lift type bioreactor and the results were 1% and 2% for low density polyethylene (LDPE)
type A and B samples with Pseudomona aeruginosa bacteria under controlled thermal
conditions.
For the low density polyethylene (LDPE) type A and B sample with Aspergillus brazilensis
fungus are 5% and 7% respectively at controlled thermal conditions. The thermal condition
favorable for microorganisms to degrade the low density polyethylene (LDPE) eciently is
22.1ºC since a degradation of 7% was obtained for the sample of low density polyethylene
(LDPE) type B with Aspergillus brazilensis.
The chemical conditions necessary for the microorganisms to degrade the low density
polyethylene (LDPE) eciently were pH and dissolved oxygen (OD), being the most
ecient pH value for biodegradation 7.14 in 7 days of duration of the process and the most
ecient dissolved oxygen (OD) value is 7.45mg/L for the sample 2 type B with Aspergillus
brazilensis.
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