**3.1 Pilot layout**

*Bacterial Biofilms*

feed pipe/effluent sieve blocking, nonhomogeneous mixing, carrier voids blocking, destroyed carriers, carrier accumulating at the effluent sieves, and carrier overflow out of reactor. These can be all prevented through skilled design, based on accumu-

as adding lime to remove calcium and magnesium could also be an option.

biofilm, leading to unfavorable condition for ammonia removal.

outer layers, making biofilms quite resilient to such disturbances.

organic load in nitrification or anammox processes that will lead to a shift in competition between heterotrophic to autotrophic bacteria. In such cases, the heterotrophic bacteria that have higher growth rate can gradually dominate the MBBR

Feed wastewater composition changes can cause disturbances such as increased

Unwanted biofilm detachment caused by toxic chemicals or abrupt operational condition changes, such as sudden increase of aeration can lead to process problems and even failure in extreme cases, but inner layers of biofilms are protected by the

This chapter provides a case study where the novel CFIC biofilm process has been studied for municipal wastewater treatment, including for organic, ammonia, and total nitrogen removal. The CFIC process operates in two modes, a normal operation where high carrier filling is applied and a washing mode for extra sludge removal (**Figure 6**). Detailed process concept description can be referred to [34], and more information is given in the following presentation of a three-stage CFIC pilot for municipal organic and nitrogen removal. The first full-scale three-stage

/d municipal wastewater

Depending on wastewater characteristics, problems such as chemical scaling on carries can happen, especially for wastewater that contains high calcium, ammonia, and other minerals, such as anaerobic digestion reject water and diary wastewater [35]. Mineral precipitation can occur when wastewater is supersaturated with relevant ion concentration [35]. The composition of mineral scaling varies and can contain struvite, hematite, hydroxyapatite, maghemite, etc. [8, 35]. Scaling on biofilm carriers creates negative effects on the reactor's performance by reducing effective surface area, hindering the mass transfer, and demanding more energy to keep the carriers in suspension. Carriers with excess scaling become heavier and settled down at the reactor bottom and need to be replaced [35]. The pH and concentration of the ions are the main factors influencing chemical precipitates on carriers. Minerals tend to precipitate more at higher pH; thus, pH control can alleviate scaling. Buffer dosing, reduced air stripping of CO2, and alkalinity removal could help to hinder scaling rates. Pure oxygen aeration is an option to avoid air stripping of CO2 to avoid pH increase. Pretreatment by chemical precipitation such

lated project knowledge and operation experience.

**10**

**Figure 6.**

**3. MBBR case study**

*The CFIC® during (a) normal operation and during (b) the cleaning cycle.*

CFIC process has also been accomplished for a 30,000 m3

treatment in Guiyang, China, in 2017.

A pilot CFIC plant with a maximum feeding capacity of 6 m3 /h has been constructed for municipal wastewater treatment study at NRA, Norway. The pilot plant constitutes of a pre-denitrification (R1), two aerobic CFIC stages (R2 and R3), and a sludge settler for sludge removal and supernatant return to biological stages (**Figure 7**). The three biological stages are 8.7, 8.3, and 8.3 m3 , respectively, in volume. Biocarriers of BWT15® and BWTX® (**Figure 3**) were filled in the first and the other two stages separately. During normal CFIC operation, a filling ratio of 62, 86, and 83%, respectively, is applied. The filling degree of the pre-denitrification was kept constant at 62% while reduced to 71 and 69% when intermittent washing cycle was performed in the other two aerobic stages.

The pilot was fed with municipal wastewater directly pumped from the full-scale primary clarifier onsite (**Figure 7**), and the wastewater characteristics are given in **Table 2**. The wastewater temperature was around 15°C in the whole year. The wastewater was fed at 3–6 m3 /h to the system with a recycle ratio of 1–1.5 during the study. To facilitate biofilm growth on carriers, washing mode was applied at the beginning of the test until stable biofilm growth was observed. The pre-denitrification stage was washed daily, and the two aerobic stages were washed together in every 1 or 2 days after the first reactor washing cycle finished. The washing cycle for each stage

**Figure 7.** *Pilot system PID layout.*


### **Table 2.**

*Feed wastewater characteristics in the two test periods.*

is normally 1 h. Wastewater samples were taken for analysis before and in the washing cycle to record parameters such as COD and suspended solid.

## **3.2 COD and ammonium removal**

Pilot performance in period 1 (**Table 2**) is presented below. Feed wastewater characteristics show that during this period more than 80% of the feed COD was particles. The influent total COD was mostly removed/retained in the denitrification reactor (R1), and the effluent TCOD in R2 and R3 is identical (**Figure 8**). Soluble COD removal was about 30%, with 16% removed in R1 and the rest was removed after R3. The feed ammonium concentration was around 20 mg/L (**Figure 9**) after combining with recycle wastewater from R3, the ammonium content was diluted to about half of initial value, and it can be seen that significant NH4-N is removed in the first (80%) aerobic reactor (R2) (**Figure 9**) to an average concentration of 1.5 mg/L. After aerobic stage 2, the NH4-N concentration was on average 0.6 mg/L. Due to very low available organic for denitrification (C to NOx-N ratio of on average 1.7), the total nitrogen removal was about 36%. Limited flow capacity of the pilot giving the TN and NH4-N loading rate about 0.4 g N/m2/d, which was much lower than previously tested (>2 g N/m2 /d in a small-scale reactor).

### **3.3 Solid removal**

Comparing to a traditional MBBR, CFIC process has good capacity to retain particles inside the carrier filter bed (instead of being continuously washed out of the system in conventional MBBR). The pilot study shows that during the MBBR mode (CFIC washing), the total suspended solid (TSS) content in the three stages was similar at around 250 mg/L, which was slightly lower than the feed TSS of about 300–400 mg/L. While in the CFIC normal operation model, the TSS was lower than 100 mg/L in all three stages with an average value of 50 mg/L. This is five times lower than a MBBR effluent TSS content, which indicates that solids were retained in the CFIC process.

CFIC washing cycle can normally bring out a large quantity of solid attached or accumulated in a short period. The average solid content for the washing water

**13**

*Biofilm in Moving Bed Biofilm Process for Wastewater Treatment*

is 1.3–6.4 times of the influent wastewater TSS in this study depending on washing frequency and accumulation of solids. The washed-out sludge has low sludge volume index (SVI) of around 70 mg/L and can settle quickly in a fast sludge settler. This feature enables at least two times smaller clarifier for sludge settlement comparing to the one needed for conventional MBBR processes. The solids

*NH4-N removal by the CFIC pilot, R1, pre-denitrification; R2 aerobic stage 1 and R3, aerobic stage 2.*

for 3–14% of the total attached TSS [36]. The washing water peak TSS content can reach over 2000 mg/L and gradually reduced with continuous wastewater feeding after washing stops [36, 37]. Over 50% of the washed-out particles are larger than 60 μm, which is larger than normal influent and effluent values [36], explaining the low SVI level. It may take 1–4 h until the effluent solid content reaches a stable

Wastewater treatment by applying biofilm has been developed over the years, and various biofilm processes are playing important roles at different stages of wastewater treatment industries. MBBR concept based on biofilm is widely used for organic and inorganic removal in both industrial and municipal wastewater remediation. It is approved to be a compact, energy-efficient, and robust solution comparing to a traditional activated sludge process. Due to biofilm growth on a protected area, different organism species coexist in the MBBR biofilm clusters which enhances their resilience to the environmental condition variations. The development based on MBBR to even compact process such as CFIC and HyVAB and the integration of MBBR with other high-rate and efficient processes could potentially reduce the footprint and complexity of wastewater treatment. Future studies to improve MBBR system for high mineral content wastewater treatment, optimize carrier designs and understand the correlation between protected area and organism species in different environmental condition, the biofilm growth, and detachment mechanisms induced by external forces and improving the energy efficiency for enhanced mass transfer

carrier surface, accounting

washed out of the system can be from 3 to 12 g TSS/m<sup>2</sup>

condition after each washing.

are interesting topics to be explored.

**4. Conclusions**

**Figure 9.**

*DOI: http://dx.doi.org/10.5772/intechopen.88520*

*Biofilm in Moving Bed Biofilm Process for Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.88520*

*Bacterial Biofilms*

**3.2 COD and ammonium removal**

lower than previously tested (>2 g N/m2

**3.3 Solid removal**

retained in the CFIC process.

is normally 1 h. Wastewater samples were taken for analysis before and in the wash-

Pilot performance in period 1 (**Table 2**) is presented below. Feed wastewater characteristics show that during this period more than 80% of the feed COD was particles. The influent total COD was mostly removed/retained in the denitrification reactor (R1), and the effluent TCOD in R2 and R3 is identical (**Figure 8**). Soluble COD removal was about 30%, with 16% removed in R1 and the rest was removed after R3. The feed ammonium concentration was around 20 mg/L (**Figure 9**) after combining with recycle wastewater from R3, the ammonium content was diluted to about half of initial value, and it can be seen that significant NH4-N is removed in the first (80%) aerobic reactor (R2) (**Figure 9**) to an average concentration of 1.5 mg/L. After aerobic stage 2, the NH4-N concentration was on average 0.6 mg/L. Due to very low available organic for denitrification (C to NOx-N ratio of on average 1.7), the total nitrogen removal was about 36%. Limited flow capacity of the pilot giving the TN and NH4-N loading rate about 0.4 g N/m2/d, which was much

Comparing to a traditional MBBR, CFIC process has good capacity to retain particles inside the carrier filter bed (instead of being continuously washed out of the system in conventional MBBR). The pilot study shows that during the MBBR mode (CFIC washing), the total suspended solid (TSS) content in the three stages was similar at around 250 mg/L, which was slightly lower than the feed TSS of about 300–400 mg/L. While in the CFIC normal operation model, the TSS was lower than 100 mg/L in all three stages with an average value of 50 mg/L. This is five times lower than a MBBR effluent TSS content, which indicates that solids were

CFIC washing cycle can normally bring out a large quantity of solid attached or accumulated in a short period. The average solid content for the washing water

*COD removal by the CFIC pilot, R1, pre-denitrification; R2 aerobic stage 1 and R3, aerobic stage 2.*

/d in a small-scale reactor).

ing cycle to record parameters such as COD and suspended solid.

**12**

**Figure 8.**

**Figure 9.** *NH4-N removal by the CFIC pilot, R1, pre-denitrification; R2 aerobic stage 1 and R3, aerobic stage 2.*

is 1.3–6.4 times of the influent wastewater TSS in this study depending on washing frequency and accumulation of solids. The washed-out sludge has low sludge volume index (SVI) of around 70 mg/L and can settle quickly in a fast sludge settler. This feature enables at least two times smaller clarifier for sludge settlement comparing to the one needed for conventional MBBR processes. The solids washed out of the system can be from 3 to 12 g TSS/m<sup>2</sup> carrier surface, accounting for 3–14% of the total attached TSS [36]. The washing water peak TSS content can reach over 2000 mg/L and gradually reduced with continuous wastewater feeding after washing stops [36, 37]. Over 50% of the washed-out particles are larger than 60 μm, which is larger than normal influent and effluent values [36], explaining the low SVI level. It may take 1–4 h until the effluent solid content reaches a stable condition after each washing.
