Similarly, values ranging from 0.09 to 0.3M for digester influent were used to model anaerobic digestion in , while the ionic strength for undigested sludge was evaluated to be 0.1M at the highest (Figure ). Some of these problems could be solved if the studies would be based on measurements of actual sludge/wastewater sample, which is not always done (64, 66, 67, 76, 81). Alternatively, the ionic strength has been derived from the conductivity in some studies . However, the linear coefficient linking conductivity and ionic strength greatly depends on the type of stream studied as discussed in , so extreme care should be taken while using this approximation.