# Demonstration of Wastewater Recycling in a Slaughterhouse
## 3 Results and Discussion
### Membrane bioreactor
Figure 11 shows the flux and the TMP during the observation period. The TMP was adjusted manually when it exceeded 1.5 bar. At the same time, a cross-flow velocity of 4.5 m\(\cdot\)s\({}^{-1}\) was ensured by a circulation pump. On day 21, a drop in the cross-flow velocity occurred due to air bubbles in the system, but this was remedied by degassing. The flux fluctuates between 25 and 50 L\(\cdot\)h\({}^{-1}\)\(\cdot\)m\({}^{-2}\); after a strong decrease, a \"cleaning in place\" was carried out with a 1% NaOH solution. For this, 200 L of the solution was circulated in the system until the pH value in the permeate no longer decreased, and the flux was restored to approximately 50 L\(\cdot\)h\({}^{-1}\)\(\cdot\)m\({}^{-2}\). As the flux was largely restored in this way, it can be assumed that mostly reversible membrane fouling had taken place up to this point. On average, about one chemical cleaning per week had to be carried out to keep the flux stable. This resulted in a chemical consumption of approximately 8 kg of NaOH and 800 L of washing water per month. Towards the end of the monitoring period, the flux dropped to 6 L\(\cdot\)h\({}^{-1}\)\(\cdot\)m\({}^{-2}\). The membrane modules were therefore dismounted and cleaned. This restored the flux. In the work of [PERSON] et al. [33], a flux of 15 L\(\cdot\)h\({}^{-1}\)\(\cdot\)m\({}^{-2}\) on  
Figure 10: Ammonium and nitrate concentrations in the aeration tank during the testing phase. average was generated in an MBR with sidestream on a laboratory scale using a hollow fiber thin-film membrane with air scouring. In a similar study by [PERSON] et al. [34], a flux of 6 L-h-1-m-2 could be stably maintained with a submerged hollow-fiber membrane module (Koch membrane systems(r)) with an outer fiber diameter of 2.6 mm, offering a filtration area of 0.5 m2 at a TSS concentration of 5 g-L-1. In the work by [PERSON] et al. [35], a flux of 50 L-h-1-m-2 was achieved with a cross-flow system on a laboratory scale at a TMP of 0.6 bar at TSS concentrations of up to 6 g-L-1 using different membranes (0.1 \(\upmu\)m polyacrylamideonitrile (PAN), 0.1 \(\upmu\)m polyethersulfone (PES), and 0.1 \(\upmu\)m polyvinylidene fluoride (PVDF) microfiltration flat sheet). A higher flux was achieved in the work of [PERSON] [36], where a peak value of 195 L-h-1-m-2 was achieved by using small sponge balls for membrane cleaning in a 1'' UF cross-flow membrane module with a cross-flow velocity of 4 m-s-1. As a result, the system investigated here is in the lower middle range for MBR applications with cross-flow filtration. Table 5 shows the performance of the MBR at the end of the monitoring period. A reduction in COD of over 90% to 80 mg-L-1 and in TN of 80% to 10 mg-L-1 was achieved. The highest TSS concentration in the reactor was 1 g-L-1, which corresponds to an average sludge load of 0.9 kgCOD-kgTS-1-d-1. In the work of [PERSON] et al. [37], the COD could be reduced to 15 mg-L-1 and the ammonium nitrogen to 0.1 mg-L-1, but a two-stage biological purification system was used here. [PERSON] et al. [7] investigated the performance of an MBR for the treatment of SWW with an initial average COD concentration of 2000 mg-L-1. A high removal efficiency of 98% was achieved. The COD concentration decreased to 25 mg-L-1. The reactor was operated at a sludge load of 0.8 kgCOD-kgTS-1-d-1 at an average TSS concentration of 3 g-L-1. This means that the COD and TN reductions were lower compared to other studies [7, 17, 37]. This could be due to the fact that the biomass concentration in the reactor was low until the end of the monitoring period and the recommended sludge load of 0.12 kgCOD-kgTS-1-d-1 [17] was exceeded. In comparison with the limit values for agricultural irrigation in Tunisia, the local requirements for water quality can be met. In comparison with the limit values applicable in the EU, it should still be verified whether the microbial parameters are compiled with and whether the limit value for nitrate of 50 mg-L-1 can be maintained permanently [38].