Commercial biogas plants: Review on operational parameters and guide for performance optimization

4. Perspective 
To sum up, operational parameters are the key factors affecting the 
mainstream biogas production process. Variations in operational pa-
rameters may induce disturbances in AD systems, stressing the under-
lying microbial community and changing internal environmental 
conditions. Proper system configuration is expected to maximize utili-
zation of process capacity and minimize internal energy consumption. 
Inadequate or faulty operating procedures resulting in large deviations 
in operational parameters from optimal ranges are the primary cause of 
frequent process instability events and indirectly lead to suboptimal 
operation of commercial biogas plants. In addition, operational pa-
rameters are greatly influenced by human manipulation, and also 
closely related to the application of different upstream substrate 
D. Wu et al.

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Fuel 303 (2021) 121282
11
pretreatments and seasonal variation. In order to maximize biogas yield 
at the industrial level, the optimization of operational parameters re-
quires comprehensive evaluation in combination with modern com-
mercial biogas plant technology and various environmental factors. 
Thus, this section presents future needs and discusses in detail the 
challenges facing biogas plants in terms of management and technical 
requirements (
Fig. 3
). 
4.1. Management requirements 
Process monitoring is widely accepted as an effective management 
strategy for optimizing AD and maintaining process stability 
[9,52]
. An 
accurate and fast monitoring and quantitation process is the main pri-
ority of control and coordination strategies. As mentioned above in 
Section 3
, the presence of insufficient process monitoring systems for 
key operational parameters can indirectly contribute to inadequate 
operational procedures and subsequent process instability. 
As reported in multiple systematic investigations, full-scale biogas 
plants have already achieved commercial online monitoring of many 
operational parameters (such as temperature, mixed liquor level, biogas 
pressure, and feeding volume) and simple state indicators (such as 
biogas yield and composition and pH) 
[9,31,95]
. However, the available 
infrastructure that can be used to achieve online monitoring varies at 
each biogas plant, with the majority requiring significant improvements. 
A possible reason for the current variable status of monitoring infra-
structure was found to lie in the different opinions of the technical 
consultants for individual plants, in addition to limits related to the scale 
and investment costs of biogas plants. In fact, it is generally feasible to 
improve the current monitoring status of the process parameters 
mentioned above, especially with respect to online monitoring. From a 
financial perspective, the complexity and cost of a monitoring system 
are directly proportional to the number of specific process parameters to 
be monitored and the proportion of those that can be monitored online. 
According to Wiese and Haeck 
[36]
, the investment cost of a process 
monitoring system in a biogas plant with an electricity generation ca-
pacity larger than 300 kW was estimated to be 5–10% of the total capital 
cost. A further financial analysis indicated that, although the operational 
cost was not included, the revenue generated for biogas plants from 
selling electricity and heat may be sufficient to cover the capital in-
vestment required for the implementation of monitoring infrastructure 
at full-scale industrial AD plants in the long term. 
In addition, for well-funded commercial biogas plants, the applica-
tion of an online diagnosis system and remote alarm system can be 
beneficial for process optimization. Combined with the response trends 
of early warning indicators (such as VFA and alkalinity 
[30,96]
) to 
process disturbances, additional information can be obtained to allow 
analysis of the rationality of the current configuration and coordination 
of operational parameters, so that operators can determine whether 
further optimization can be conducted, or whether precautionary 
countermeasures (such as decreasing the OLR or increasing mixing 
duration) should be applied in advance to prevent imminent process 
instability. 
Another important management requirement, especially for small- 
scale biogas plants, is operator training. In New York State, nearly all 
active on-farm AD systems are operated by a farm worker who usually 
has no previous experience or training related to AD. Moreover, in 
addition to daily farm-related work, the plant operator must operate, 
maintain, and monitor AD and combined heat and power (CHP) systems 
without support from other personnel 
[34]
. Considering the complexity 
of AD, process monitoring strategies and related supporting equipment, 
the presence of relatively untrained biogas plant operators indirectly 
contributed to the frequent occurrence of process instability and low 
operational efficiency. Thus, more attention should be paid to ensure 
that the operators of commercial biogas plants receive adequate 
training.