Waste Activated Sludge Production Research Articles

Electricity production and sludge reduction by integrating microbial fuel cells in anoxic-oxic process

To produce energy and reduce sludge production from the treatment of municipal wastewater, four identical microbial fuel cells (MFCs) were constructed in an anoxic–oxic (A/O) process (MFCs-A/O system). Experimental results indicated that this system enhance the removals of chemical oxygen demand (COD) and total nitrogen (TN). The electricity produced by each MFC were ranged from 0.371 to 0.477V (voltage) and from 138 to 227mW/m3 (power density) at the stable stage, when the external resistance was fixed at 1000Ω. The coulombic efficiency of the MFCs-A/O system ranged from 0.31% to 1.68% (mean=0.72%) at the stable stage, respectively. The removals of COD and TN in the MFCs-A/O system were slightly higher than those in the control system. Compared with the control system, the MFCs-A/O system can reduce waste activated sludge production and sludge yield by 24.0% and 24.2%, respectively. The experimental results indicated that the MFC constructed in A/O system improves wastewater treatment and the MFCs-A/O system can produce electricity while reducing sludge production and increasing wastewater treatment efficiency.

Treatment of waste activated sludge together with agro-waste by anaerobic digestion: focus on effluent quality

Waste activated sludge production and management plays an important role in wastewater treatment plants (WWTPs), especially from an economic point of view. One possible approach is the anaerobic co-digestion of waste activated sludge with others organic substrates in mesophilic and thermophilic conditions in order to exploit the spare volume of existing reactors, recover energy from biogas production, and obtain a fertilizer as final product. The anaerobic trials were carried out at pilot scale, applying two organic loading rates (2.8 and 4.5 kg chemical oxygen demand (COD)/(m(3)·d)) with a hydraulic retention time of 16 and 21 days. Among agro-wastes, wine lees were chosen because of their continuous availability throughout the year, and their high COD content (up to 200-300 g/l, 70% soluble, on average). The addition of wine lees to activated sludge determined a higher biogas production (best yield was 0.40 Nm(3)/kgCOD(fed)) improving the energetic balance of the sludge line of the WWTP. The characterization of both substrates fed and digester effluents was carried out in terms of heavy metals; comparison with EC proposed limits showed that, due to high content of Cu in wine lees, the loading rate of this agro-waste should be limited to maintain good characteristics of final biosolids.

Pilot-Scale Waste Activated Sludge Alkaline Fermentation, Fermentation Liquid Separation, and Application of Fermentation Liquid To Improve Biological Nutrient Removal

The use of sludge fermentative short-chain fatty acids (SCFA) as an additional carbon source of biological nutrient removal (BNR) has drawn much attention recently as it can reuse sludge organics, reduce waste activated sludge production, and improve BNR performance. Our previous laboratory study had shown that the SCFA production was significantly enhanced by controlling sludge fermentation at pH 10 with NaOH. This paper focused on a pilot-scale study of alkaline fermentation of waste activated sludge, separation of the fermentation liquid from the alkaline fermentation system, and application of the fermentation liquid to improve municipal biological nitrogen and phosphorus removal. NaOH and Ca(OH)(2) were used respectively to adjust the alkaline fermentation pH, and their effects on sludge fermentation and fermentation liquid separation were compared. The results showed that the use of Ca(OH)(2) had almost the same effect on SCFA production improvement and sludge volatile suspended solids reduction as that of NaOH, but it exhibited better sludge dewatering, lower chemical costs, and higher fermentation liquid recovery efficiency. When the fermentation liquids, adjusted with Ca(OH)(2) and NaOH respectively, were added continuously to an anaerobic-anoxic-aerobic municipal wastewater BNR system, both the nitrogen and phosphorus removals, compared with the control, were improved to the same levels. This was attributed to the increase of not only influent COD but also denitrifying phosphorus removal capability. It seems that the use of Ca(OH)(2) to control sludge fermentation at pH 10 for efficiently producing a carbon source for BNR is feasible.

The effect of flow equalisation and prefermentation on the sludge production and sludge characteristics in a BNR plant

A full-scale study investigated the influence of diurnal flow equalisation and prefermentation on the characteristics of sludge. The diurnal variations in the sludge concentration and the level of sludge blanket in the secondary clarifiers were evened out significantly with the use of an equalization basin. Stable conditions in the aeration basin and in the secondary clarifiers contributed to the improvements in the performance of the BNR plant. A decrease in the waste activated sludge production and an improvement in the settleability were also observed. The low WAS yield was attributed to the low yield COD compounds produced by the prefermentation, longer sludge age and constant conditions obtained by the flow equalisation. Some evidence was found that good settling properties would be related to the amount of suspended solids fed to the biological process as well as to the good performance of the biological process.

Treatment of mixed municipal and winery wastewaters in a conventional activated sludge process: a case study

The possibility of co-treating municipal and winery wastewaters in a conventional activated sludge process was studied at full scale. The wastewater treatment plant considered in this paper operated an extended-oxidation process during vintage (four month per year) and a pre-denitrification/ oxidation process during the rest of the year. The experimentation showed that good performances, in terms of COD and nitrogen removal, could be obtained in both cases: 90% and 60%, for COD and nitrogen removal, respectively. Thanks to the high solid retention times applied to the system (up to 48 days) the waste activated sludge production was low (0.20 kgMLVSS/kgCODremoved) and respiration was the main process for carbon removal. Nitrification was always satisfactory while the behaviour of the denitrification process during vintage was not totally understood and further studies are going on.

Waste activated sludge production of the enhanced biological phosphorus removal process

The effect of the enhanced biological phosphorus removal process (EBPR) on waste activated sludge (WAS) production and the type of phosphorus storage were investigated in two continuous‐flow activated‐sludge systems in a semitechnical scale. One of the plants was operated with the A/O® process, whereas the other plant was operated in a conventional, fully aerobic mode and served as a control. By monitoring the elementary composition of the activated‐sludge solids in plant II and by using phosphorus fractionations, it was found that nearly all of the enhanced phosphorus removal was due to storage as polyphosphate (poly‐P). The additional uptake of phosphorus resulted in an increase of the inorganic sludge mass, which was determined to be 3.05 g suspended solids (SS)/g P using the results of the measurements of the nonvolatile solid fraction. This value was confirmed experimentally by the measurement of the difference between the WAS production of plant I and plant II. Based on the specific WAS production, an additional dry solids production of 3.14 g SS/g P was calculated. No indications for a significant difference of the organic sludge production between both plants were found, although the organic WAS production was slightly higher in experimental periods with a relatively high phosphorus content of the activated‐sludge solids of plant II.

Influence of the enhanced biological phosphorus removal on the waste activated sludge production

The effect of the enhanced phosphorus removal process (EBPR) on the waste activated sludge production and the type of phosphorus storage were investigated in two continuous flow activated sludge systems on semi-technical scale. One of the plants (plant II) was operated with the A/O process, whereas the other plant (plant I) was operated in a conventional, fully aerobic mode and served as a control. By monitoring the elementary composition of the activated sludge solids in plant II it was proved that a major part of the enhanced phosphorus removal was due to a storage as polyphosphate (poly-P). The additional uptake of phosphorus resulted in an increase of the inorganic sludge mass which was determined as 3.05 g SS/g P using the results of the measurements of the non volatile solid fraction. This value was also experimentally confirmed by the measurement of the difference between the WAS production of plant I and plant II. Based on the specific WAS production, an additional dry solids production of 3.14 g SS/g P was calculated. No indications for a significant difference of the organic sludge production between both plants were found, although the organic WAS production was slightly higher in experimental periods with a relatively high phosphorus content of the activated sludge solids of plant II.

Influence of the enhanced biological phosphorus removal on the waste activated sludge production

The effect of the enhanced phosphorus removal process (EBPR) on the waste activated sludge production and the type of phosphorus storage were investigated in two continuous flow activated sludge systems on semi-technical scale. One of the plants (plant II) was operated with the A/O process, whereas the other plant (plant I) was operated in a conventional, fully aerobic mode and served as a control. By monitoring the elementary composition of the activated sludge solids in plant II it was proved that a major part of the enhanced phosphorus removal was due to a storage as polyphosphate (poly-P). The additional uptake of phosphorus resulted in an increase of the inorganic sludge mass which was determined as 3.05 g SS/g P using the results of the measurements of the non volatile solid fraction. This value was also experimentally confirmed by the measurement of the difference between the WAS production of plant I and plant Il. Based on the specific WAS production, an additional dry solids production of 3.14 g SS/g P was calculated. No indications for a significant difference of the organic sludge production between both plants were found, although the organic WAS production was slightly higher in experimental periods with a relatively high phosphorus content of the activated sludge solids of plant II