Dewatering, Stabilization, and Final Disposal of Waste Activated Sludge in Constructed Wetlands

Objective: This research aimed to assay the dehydration and stabilization of surplus biosolids from a wastewater activated sludge treatment plant, with sludge-treatment wetlands, at the Iguazú National Park (Misiones, Argentina). Materials and Methods: A 12-cell sludge-treatment reed beds (STRB) system was built and operated for four years. Afterwards, the accumulated sediments were analyzed for total solids (TS) concentration, volatile solids (VS) reduction, specific oxygen-uptake rate (SOUR), and heavy metals and pathogens concentrations. Results and Discussion: TS concentration increased from 0.55 % to 14.3 %, VS were reduced by 33.3 %, and SOUR lowered to 1.09 mg O2gTS-1 h-1. These figures and the final concentrations of heavy metals and pathogenic microorganisms (102 MPN E.coli.gTS-1) indicated a degree of stabilization and sanitation that allowed classifying these biosolids as Class A, according to the Argentine guidelines, National Resolution 410/18, and enabled their reuse for soil amendment in landscapes and other agronomic purposes. Conclusion: The technology tested showed good results applied under a tropical climate, with annual temperatures between 17 and 27 °C, rainfall of 1870 mm y-1, and planted with autochthonous vegetation. Furthermore, it allowed the reuse of 221 t (144 m3) of a harmless product in an environmentally sustainable way.

Achieving enhanced biological nitrogen removal via 2450 MHz electromagnetic wave loading on returned sludge in anaerobic-anoxic-oxic process

To evaluate the enhancing of the biological nitrogen removal effectiveness by electromagnetic wave loading on returned sludge in the A/A/O reactor, some experiments were completed with the returned sludge loaded by 2,450 MHz electromagnetic wave. The excess sludge yield and pollutant removal effect of the system were evaluated. Results showed that stronger denitrification effect and less sludge yield were achieved. When 30% of the returned sludge was loaded by electromagnetic wave, the actual denitrification efficiency increased by 7% without dosage. The dissolution of carbon, nitrogen and phosphorus from loaded returned sludge was detected, thus providing the system with a supplemental carbon source of 4.6 g/d SCOD. The specific oxygen uptake rate of the oxic activated sludge increased by 14%, and the denitrification rate of the anoxic activated sludge increased by 29%. Illumina MiSeq analysis showed that the microbial richness increased obviously, and denitrifying bacteria (i.e. Dechloromonas, Zoogloea and Azospira, etc.) were accumulated.

Critical design factors for polyvinyl alcohol hydrogel entrapping ammonia-oxidizing bacteria: biomass loading, distribution of dissolved oxygen, and bacterial liability

The single-stage configuration of the partial nitritation (PN)–anaerobic ammonium oxidation (AMX) process is preferred due to low pH fluctuation and the low concentration of inhibitory NO2-. The novel core-shell structure integrates ammonia-oxidizing reaction in the outer layer to protect AMX bacteria in the core gel bead from oxygen inhibition and provide NO2-. Here, the initial activity of ammonia-oxidizing bacteria (AOB) in the outer layer was assessed by the specific oxygen uptake rate (OUR). AOB activity was positively correlated with biomass loading in the outer layer. A maximum OUR of 10.5 mg-DO/L∙h was achieved with AOB loading of 0.23 mg-VSS per bead. During AOB enrichment, the NO2- production rate was linearly increased up to 0.65 kg-N/m3-d for 17 days (PVA hydrogel packing ratio=17%). The maximum oxygen penetration depth (OPD) was reduced from 966.7±52.3 μm before enrichment to 333.3±36.4 μm after the AOB enrichment. The liable bacteria were observed within a range of 165 μm of the outer layer using the live and dead cell staining. Based on the OPD and liable cell distribution results, a minimal outer layer thickness of approximately 350 μm was suggested to facilitate a successful PN–AMX process.

Experimental Investigation of Substrate Shock and Environmental Ammonium Concentration on the Stability of Ammonia-Oxidizing Bacteria (AOB)

A wastewater treatment plant (WWTP) frequently encounters fluctuation in ammonium concentration or flow rate (Q), which may affect the stability of ammonium oxidizing bacteria (AOB). In this study, two continuous stirred tank reactors (CSTRs) were operated for 588 days and ammonium concentration was varied at various steady-state conditions. There was no inhibition observed in CSTR operation and AOB acclimated once at a certain ammonium concentration. Cells at an acclimated steady-state concentration (200 mgTAN/L from R(A) and 1000 mgTAN/L from R(B)) were extracted to perform a batch test at operating conditions, and self-inhibition behavior was observed in the batch reaction. In CSTR operation, the environmental ammonium concentration was varied and the specific oxygen uptake rate (SOUR) value was estimated from daily profile data and compared with batch reaction. In the CSTR operation as a substitute for self-inhibition, the SOUR was shifted towards the maximum specific oxygen uptake rate (SOURmax) and no self-inhibition was observed. For further justification of the CSTR’s stability, several total ammonium nitrogen (TAN) concentrations (range from ~−106 to ~+2550 mgTAN/L) were directly added to interrupt the stability of the process. As a substitute for any effect on the SOUR, the CSTRs were recovered back to the original stable steady-state conditions without varying the operational conditions.

Specific Oxygen Uptake Rate and Mass Transfer Coefficient in Activated Sludge System

Activated sludge process is one of the effective methods in biological wastewater treatment and the impact of oxygen transfer through aeration process has the most important breakthroughs as it served as the largest consumer in the treatment. Aeration is an energy demanding process. Oxygen transfer into an activated sludge is a very challenging issue in the field of multiphase flows. Apart from the physical mass transfer phenomena between gas, liquid and solids phases, the transport mechanisms are also overlapped by time and temperature, varying microbial activity, impurity loads, adsorption and desorption processes. Oxygen uptake rate (OUR) for microbial population in the activated sludge system is important parameter to determine the amount of oxygen consumed during aerobic heterotropic biodegradation in the system. Evaluation of specific oxygen uptake rate (SOUR) and the volumetric mass transfer coefficient (KLA) of oxygen for three different wastewater treatment processes, namely conventional activated sludge (CAS), oxidation ditch (OD) and sequencing batch reactor (SBR) treating municipal wastewater in Kuala Lumpur have been carried out. In-situ and ex-situ measurement of pH, dissolved oxygen (DO), temperature, MLSS and MLVSS were carried out. In the activated sludge treatment, very low concentration of dissolved oxygen may cause the wastewater to turn septic resulting in death of bacteria or in active due to unstable anaerobic conditions. Conversely, an excessive dissolved oxygen may result to high energy and high 25 operating cost. Higher flowrate may also cause dissolved oxygen to rise, reducing the quality of sludge and slowing the denitrification process in the system. Results revealed that the OUR for SBR, OD and CAS were 9.582 mg O2 /L/hr, 10.074 mg O2 /L/hr and 13.764 mg O2 /L/hr, respectively. Low oxygen uptake rate indicates a low rate of microbial respiration. By computing the OUR, the mass transfer coefficient could be evaluated. It should be noted that among the treatment system in this study, the conventional activated sludge shows the highest mass transfer coefficient and specific oxygen uptake rate of 2.038 hr-1 and 15.605 mg O2 /g MLVSS/hr, respectively. Improving the oxygen transfer rate and reducing aeration in the system could achieve a cost-effective aeration system.

Microbial Strategies for Cellulase and Xylanase Production through Solid-State Fermentation of Digestate from Biowaste

Solid-state fermentation (SSF) is a promising technology for producing bioproducts from organic wastes. The objective of this study is to assess the feasibility of using digestate as substrate to produce hydrolytic enzymes, mainly cellulase and xylanase, by exploring three different inoculation strategies: (i) SSF with autochthonous microbiota; (ii) non-sterile SSF inoculated with Trichoderma reesei and (iii) sequential batch operation to select a specialized inoculum, testing two different residence times. Native microbial population did not show a significant cellulase production, suggesting the need for a specialized inoculum. The inoculation of Trichoderma reesei did not improve the enzymatic activity. On the other hand, inconsistent operation was achieved during sequential batch reactor in terms of specific oxygen uptake rate, temperature and enzymatic activity profile. Low cellulase and xylanase activities were attained and the main hypotheses are non-appropriate biomass selection and some degree of hydrolysis by non-targeted proteases produced during fermentation.

Liquid-Phase Respiration Activity Assays to Assess Organic Waste Stability: A Comparison of Two Tests

The stability of twenty seven composts and organic substrates (including raw, less stable and stable materials) was assessed using two different liquid phase tests were carried out. One of the tests was introduced in 1998 and was based on the calculation of a Specific Oxygen Uptake Rate (SOUR). The newly introduced liquid phase test presented here is simpler to set-up and to perform that the older liquid phase test. It is based on the quantification of oxygen consumption in the headspace of a BOD bottle that contains the liquid-solid solution. The results indicate that a marginal correlation does exist between the main indices calculated from both tests. The correlation was stronger for the indices calculated for stable-processed organics than for the raw (unprocessed materials). The SOUR ranged from 1520 to 3650mg O2/kg VS-h for the raw materials and from 110 to 1150 mg O2/kg VS-h for the processed materials, respectively. The corresponding stability rate related index (LSRI24) of the new liquid phase test introduced here ranged from 240 to 1180 mg O2/dry kg-h for the raw materials and from 64 to 792 mg O2/dry kg-h for the processed ones.

Aktivitas Mikroba Lumpur Aktif Konsentrasi Tinggi Pada Sistem Lumpur Aktif- Membran

Pengolahan air limbah dengan sistem kombinasi proses lumpur aktif dengan membrane telah banyak dimanfaatkan di beberapa negara maju. Sistem ini diketahui mampu beroperasi dengan konsentrasi lumpur aktif (MLSS, Mixed Liquor Suspended Solid) sangat tinggi sehingga menghasilkan sistem yang kompak dengan efisiensi pengolahan tinggi. Penelitian ini mengkaji aktifitas mikroba yang terlibat dalam sistem. Aktifitas yang dikaji antara lain laju pemanfaatan oksigen spesifik (SOUR, specific oxygen uptake rate), parameter kinetika, serta laju pemanfaatan nitrogen dan fosfor.Proses pengolahan berjalan pada konsentrasi MLSS jauh di atas proses lumpur aktif konvensional, yaitu berturut-turut 18.400, 22.900, 24.300, dan 25.500 mg/l. Untuk mendapatkan konsentrasi MLSS tersebut, proses pengolahan beroperasi pada waktu tinggal cairan (HRT, hydraulic retention yime) 24 jam dan waktu tinggal sel (SRT, solid retention time) 8, 16, 24, dan 32 hari. Hasil penelitian menunjukkan bahwa mikroorganisme yang terlibat pada proses ini ditandai oleh mikroorganisme yang mempunyai laju pertumbuhan sangat lambat. Parameter kinetika yang diperoleh sebagai berikut: laju pertumbuhan maksimum spesifik (μmax) 0,024 jam-1, koefisien perolehan sel (Y) 0,515 (mg sel/ mg COD), konstanta setengah jenuh (Ks) 589 mg/l, dan laju kematian spesifik (b) 0,010 jam-1. Dengan semakin tinggi konsentrasi lumpur aktif, maka aktifitas mikroba akan semakin kecil. SOUR yang diperoleh untuk SRT 8,16,2 dan 32 hari berturut-turut sebesar 0,612; 0,357; 0,279; 0,207 gO2 / (gMLSS.hari). bila ditinjau dari segi operasionalisasi unit pengolahan limbah, maka proses pengolahan lumpur aktif – membran jauh lebih menghemat kebutuhan nitrogen dan fosfor untuk nutrient.Kata kunci : aktifitas mikroba, sistem lumpur aktif-membran, SOUR

Investigation of α-Amylase Production with Bacillus amyloliquefaciens in a Cocurrent Downflow Contacting Reactor

The cocurrent downflow contacting reactor (CDCR) has a high oxygen transfer rate by providing the effective the gas-liquid contact. This property is an advantage for enzyme production. In this study, the CDCR was used for the production of α-amylase by Bacillus amyloliquefaciens for different starch concentrations in the range of 7.5–17.5 g l–1 at constant air and liquid flow rates. The values of the volumetric oxygen transfer coefficient (kLa) and specific oxygen uptake rate ( ${{\rm{q}}_{{{\rm{O}}_2}}}$ ) were determined during enzyme production. It has been found that the starch concentration has great effect on the enzyme activity. Maximum enzyme activity (1,000 IU ml–1) was obtained in the fermentation broth containing of 15 g l–1 starch concentration at 37 °C and pH 7 for 28 h. The kLa and ${{\rm{q}}_{{{\rm{O}}_2}}}$ values were determined to be 175.83 h–1 and 47.5 mg O2 g–1cell h–1, respectively.