Mini Review
The popularity of the
circular economy is due to the increasing amount of waste-produced in the
agro-food processing industry; new solution of waste recycling with biotech
innovation are available. In the EU 3.5 ton per capita of waste are annually
produced, including more than 400kg per person per year of domestic waste. The
projections suggest that this increase at worldwide level, will continue at
least until 2030 and there is no real evidence of decoupling between waste and
economic growth despite progresses in waste recycling. While all sectors are
potentially eligible for funding under the Eco-innovation initiative, certain
activities have been singled out as priority areas because of their
considerable impact on the environment and their potential contribution to
meeting the EU’s own environmental objective. In the modern Agro-food system,
the proper treatment of organic effluents to avoid their discharge as sewage
water or sewage sludge, to prevent the pollution of the ground and water
resources (oceans, lakes, rivers) is becoming especially important. Water is
essential not only for direct uses, but also for ensuring the integrity of the
ecosystems and the goods and services they provide to humans. The case we have
considered is the whey, a by product of the cheese production, requiring urgent
solutions to improve water efficiency and water quality used in the cycle.
The Cheese Manufacturing and Whey Processing
Cheese whey (CW) is the
liquid part after milk has been curdled and strained in cheese production; it
is the main by-product of the cheese making [1] After coagulation casein curd
separates from the milk, under the action of chymosin or mineral/organic acid
producing; the remain is the whey, a watery and thin liquid solution.
Approximately from ten parts of milk, one part of cheese and nine parts of whey
are produced with appreciable quantity of water soluble components [2]. It is
estimated that the whey produced annually by the European dairy industry is
about 75 million tons. it is a by-product of cheese making process, in the past
it was discharged as waste into soil, rivers, lakes, causing pollution. When
poured into a waterway, or sewer, the whey can deplete the water oxygen levels,
causing serious environmental damage. The whey pollution is measured by the BOD
and COD indexes (1.18) many authors have reported the following results: BOD5
varies between 30 and 60 thousand ppm (35-45 kg/m3) while COD varies between 50
and 100 thousand ppm.(50-100Kg/m3 ). According to Siso, only 50% of the total quantity
of CW is treated and turned into non polluting products, then the whey
wastewater disposal of the whey is becoming a major environmental problem in
the world with the production of cheese whey is estimated over 108 tonnes per
year. The whey dispersion is now forbidden by recent legislation act. In Italy
in 2015, 1.2 million tons of cheese and 9.5 million tons of whey were produced;
in most of the northern regions the conversion ratio cheese/milk was around 1.1
to 10 due to the prevailing medium hard cheese while in the south the ratio
around 1.4 to 10 for the prevailing production of mozzarella cheeses. The hard
and semihard cheeses represent the 59% of Italian production, followed by fresh
and soft cheeses, with 41%. Four Italian regions located in the northern
regions: Lombardia, Emilia Romagna, Veneto and Piemonte produce almost seven
million ton of whey representing the 72% of the total amount. Grana Padano is
the most diffused hard cheeses accounting for 22% of total milk output. The
first step of whey processing is the separation of the retentate fraction
containing proteins from permeate fraction containing lactose; different
methods are now available as ultrafiltration, diafiltration, inverse osmosis
and nanofiltration. Our interest in Lactose is for its use in production of
biopolymer namely PHA group after fermentations. PHA (polyhydroxy-alkanoate) is
a collective name for a family of biodegradable intracellular bio-polymers made
of chemically similar building blocks. PHB (poly-3-hydroxybutyrate) is the most
widespread member of the PHA family produced by a wide range of prokaryotic
genera starting from renewable feedstocks. A particular characteristic of PHA
is its biocompatibility, making them suitable for medical applications. PHA
also has good barrier properties, of interest for food product packaging. For
these reasons, applications of PHA are found, for instance, in single-use
packaging films, bags, containers, paper coatings, agricultural foils,
biodegradable carriers for long-term dosage of compounds like drugs or
fertilizers, and medical applications like surgical pins, sutures, wound
dressings, bone and blood-vessel replacements. Currently, the industrial
production of PHA by fermentation, is still a guess in terms of yield,
extraction and economic sustainability as the production cost of plastics from
petrochemical product is still more competitive and preferred by industrial
companies compared to biopolymer production, however the two costs are
converging rapidly. The environmental problems associated with the accumulation
of traditional petrol derived plastics, due to the long-term degradation, makes
urgent to find convenient bioplastic processing. The PHAs are polymers of
carbon and reserve of energy accumulated in the cytoplasm of many bacterial
species under particular conditions of excess of carbon availability, while
some other factors are limiting (i.e. N, P, S, and other). These polymers can
be synthesized in different types of PHA that microorganisms accumulate as
insoluble inclusion in their bodies. The production of PHA from cost-effective
substrates, such as agro-industry residues and specifically the whey is the
interest of many researchers, interested in the dairy chain optimization and
sustainability. The whey is a by-product of the cheese production chain; in
volume represents the 80-90% of the milk converted into cheese. Sweet skimmed
whey is subjected to a concentration step, removing 80% of its water content. A
convenient solution is to extract proteins from retentate fraction and sell
into separate market outlets. The permeate fraction rich in lactose
(45gr/liter) is a carbon source for different metabolic pathways. We
concentrate in the lactose fermentation to produce PHA; a number of studies
identified many microbial groups able to synthesize these polymers, the most
important are the Rastonia group, the Escherichia coli, the Capriovidus
Necator. These bacterial species are the most used for industrial application
since they associate high productivity and reduced times of PHA accumulation.
The PHA accumulation speed is very variable: specific rate 0.15 g/g*h
equivalent to 15% yield per hour; 16.8 g/L biomass containing 73% PHA were
obtained Koller [3].
Biodegradability
Majority of the strains
that are able to degrade PHA belong to different taxa such as Gram-positive and
Gram-negative bacteria, Streptomyces and fungi. It has been reported that 39
bacterial strains of the classes Firmicutes and Proteobacteria can degrade PHA,
PCL, and PBS, but not PLA. The population of aliphatic polymerdegrading
microorganisms in different ecosystems was found to be in the following order:
PHA > PCL > PBS > PLA. Microorganisms secrete enzymes that break down
the polymer (PHA depolymerize) into its molecular building blocks, called
hydroxyacids, which are utilized as a carbon source for growth. While
degradation by mesophilic temperatures, microorganisms which are capable of
degrading various kinds of polyesters at high temperatures are of interest. A
thermos-tolerant Aspergillus sp. was able to degrade 90% of PHA film after five
days cultivation at 50 °C. In the 1980s, Imperial Chemical Industries developed
poly (3-hydroxybutyrateco3- hydroxyvalerate) obtained via fermentation that was
named ‘Biopol’. It was sold under the name ‘Biopol’ and distributed in the U.S.
by Monsanto and later Metabolix.
Researchers in industry
processing are working on methods with which transgenic crops will be developed
that express PHA synthesis routes from bacteria to produce PHA as energy
storage in their tissue. Commercial ventures scaling up PHA production using
fermentation processes include Telles, USA; Biomer Biotechnology Co., Germany;
PHA Industrial, Brazil; Mitsubishi Gas Chemical, Japan; Kaneka, Japan;
Biomatera, Italy; Jiangsu Nantian Group, China; Tianan Biologic Material,
China; and Lianyi Biotech, China. PHAs is a very versatile precursor of
bio-plastic materials that raise the attention of different industrial
branches. As the best-known and most simple application, these biopolymers are
of interest for packaging purposes, especially in such areas where compostable
packaging is wanted, e.g. in the food producing industry. Especially in the
field of packaging of easily spoiling food, the high oxygen barrier of PHA
films is very beneficial. In addition, bottles for shampoos (Wella, Germany)
made of PHAs were commercially available in the past. PHAs can be used for
paper coating, production of daily commodity items like razors, diapers,
hygiene products, or cups and dishes (Metabolix, USA; BASF, Germany). For these
applications, PHAs can be processed by techniques of injection moulding or film
blowing using the same equipment as known from the well-established processing
of petrochemical plastics. In the medical field, PHAs were already investigated
as bone implant materials, for tissue engineering, for in-vivo application as
implants, surgical pins, screws, meshes and sutures, and as carrier matrices
for controlled drug release. Also the production of highly sophisticated
surgical articles such as artificial blood vessels and vein valves, spinal
fusion cages, bone marrow scaffolds, and meniscus regeneration devices.
Especially the possibility to change the composition of PHA allows the
manufacture of materials with tailor-made mechanical properties and a fine-tuned
degradation rate under in-vivo conditions.
Economic Caveat
Three main problems have
to be afforded to make the bioplastic production feasible:
i. cost of feedstock
ii. cost of downstream
process
iii. Industrial cost and
optimal scale. The feedstock costs are limited by the need to recycle a great
amount of whey in intensive cheese production.
By the way marketing
opportunities for whey proteins and lactose are growing and compete with PHA
production. The 2nd problem is the optimization of the downstream processing
for PHA recovery and refining after cell harvest. As intracellular products,
PHAs have to be separated from the surrounding non-PHA cell mass, mainly
consisting of proteins, lipids, nucleic acids and special polysaccharides.
Here, high input with often highly polluting solvents and enormous energy
demand still are the caveat in PHA recovery, compromising the demanding claims
of these bio-plastics to be ecologically sound materials. The 3rd problem
implies to afford the increasing productivity by designing the optimal
engineering plant for the final break-through of these biopolymers on the
market. A continuous biotechnological production process is well known as an
interesting solution for achieving high productivity, lower costs and constant
product quality. Some authors reported high productivities of 1.85g/L h for PHB
and a constant and satisfying product quality using Cupriavidus necator strain.
To optimize the entire
PHA chain, we suggest the following steps:
a) Optimize the
collection whey costs from a basin area of enough size to cover the costs and
minimize the environmental cost of transport [4].
b) stabilize the whey
quality and improve the efficiency of the whey processing through advanced
membrane methods of ultrafiltration, nanofiltration, inverse osmosis.
c) Find new bacterial
strain to convert directly and more efficiently the lactose into PHA, avoiding
the feast-famine two step fermentation.
d) optimize the scale of
the chain. Some industries achieved the break point of biopolymer cost
production with traditional plastic derived from petroleum (around 1.5 /Kg)
with scale production of 40 thousand ton per year [5-7].
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