Waste Management Methods for Disposables
The most common methods for disposing of single-use plastics are landfill and incineration, with incineration being more popular.
In some cases, incineration can also result in significant energy savings through cogeneration techniques,3 in which a facility captures the energy generated from burning its waste and uses it to produce heat or electricity.
The possibility of recycling has been assessed by some suppliers, but recycling opportunities are extremely limited, primarily
because of the multilayer films of which disposable bag systems are made. Disposable bag films often combine polyethylene,
polypropylene, ethylene vinyl acetate, and nylon. It would be more feasible to recycle the silicone tubing that is often attached
to bag systems, but that would require segregating tubing and bag, the logistics of which are not simple. In addition, recycling
may require pretreatment of biohazardous single-use materials, depending on the process step for which the disposable equipment
was used. The combination of these factors makes it extremely difficult to develop an economically viable case for recycling
disposable technologies in their current configuration. In a recent article, however, Millipore's Director of Sustainability
David Newman suggested that homogenous or separable materials (in disposable filters, for example) could increase the feasibility
of recycling.4 The environmental impact of disposables could also be reduced by packaging components in bulk, instead of individually,
to decrease the amount of packaging.
Basis of Analysis
Taking into account the current state of disposable technology implementation and the disposal methods described above, we
have compared the environmental impact of a commercial MAb process, working with either stainless steel or disposable technologies,
looking specifically at the relative environmental footprints of both facilities.
The environmental impact of the traditional stainless steel–equipped and disposables-based facilities has been evaluated using
a model based on a commercial MAb process at 3 x 2,000 L scale.5 The main difference between the two manufacturing options is that one uses stainless-steel equipment and the other implemented
disposable bags, tubing, and associated components for:
- cell culture bioreactors
- mixing solutions (buffer and media)
- holding solutions (buffer and media)
- product hold
- liquid transfer tubing and filters.
The stainless-steel equipment requires cleaning after each use. The buffer vessels are cleaned using a simple rinse cycle.
The cell culture bioreactors, product, and media vessels are cleaned using a more rigorous cleaning cycle, which includes
a purified water (PW) rinse, caustic clean, acid clean, another PW rinse, and a final rinse with water for injection (WFI).
Bioreactors and vessels that undergo a full cleaning cycle also require sanitization with steam.
In the disposables-based facility, single-use bag systems are used to prepare and store media, buffers, and products before
further processing. The bag systems are provided presterilized, ready for process use, and are not used again; hence, no cleaning
operations are required.
In this study, we have focused mainly on the process and the key areas that are affected by choosing disposable equipment,
such as facility size, utilities, consumables, and labor requirements. It was not our intention to evaluate materials that
are common to both operations. In addition, we have not examined the heating and cooling loads associated with heating, ventilation,
and air conditioning (HVAC) systems, instead restricting our HVAC data to the loads needed to run fans. In this way, we eliminated
regional factors resulting from climate differences, although this will be to the detriment of the disposables facility. The
analysis has not taken into account general cleaning, clothing wash up activities, or the disposal of single-use garments.
The single-use plant should have a smaller footprint in these areas because there are fewer employees. The study, therefore,
only considers differences in the use of consumables (e.g., disposable bags); we did not account for disposables that are assumed to be the same in
both facilities. These include small-scale cell culture equipment (e.g., single-use flasks, filters, and pipette tips); filters
(e.g., liquid sterile filters, depth filters, UF–DF cartridges); and other common disposable items (e.g., gloves, isopropyl
alcohol wipes for cleaning, weigh boats).
Table 1. Key parameters for comparing the environmental impact of disposables-based and stainless steel–based facilities
Table 1 provides a description of the key comparison parameters. The resulting data sets from the model are then used to evaluate
the carbon footprint. The basis for the carbon footprint estimation is summarized in Table 2. The analysis will also take
into account differences in carbon emissions that could result from different electricity sources, depending on whether the
electricity was generated from: (1) firing coal, (2) firing natural gas in a combined cycle, or (3) the average mix of US
sources (coal, gas, hydroelectric, nuclear, other).
Table 2. Bases for estimating energy consumption and carbon emissions