High Suspended Solids Research Articles

Evaluating the plant response of MLSS (Mixed liquor suspended solids) based biofertilizers in tomato

Mixed liquor suspended solids (MLSS) is the concentration of suspended solids in an aeration tank during the activated sludge process, which occurs during the treatment of waste water. Mixed liquor is a combination of raw or unsettled wastewater or pre-settled wastewater and activated sludge within an aeration tank. MLSS consisted mostly of microorganisms and non-biodegradable suspended matter. Unlike previous research, this study aimed at evaluating the possibility of using primary wastewater from aeration tank containing high suspended solids (MLSS) from paper factory as the whole nutrients source for beneficial microbial growth. The beneficial microbes were then mixed with suitable carrier and used for plant growth promotion. The results of the above study revealed that the MLSS based biofertilizer was equally efficient with conventional biofertilizers in promoting the germination and growth of tomato.

Start-up treatment of palm oil mill effluent (POME) final discharge using Napier Grass in wetland system

Average of about 53 million m3 POME is being produced yearly in Malaysia. The treated palm oil mill effluent (POME) will be discharged to the river. However, the POME final discharge still contains high oxygen demand (COD) and suspended solids (SS) that potentially to cause environmental issues. Therefore, the aim of this study is to treat the POME final discharge with Napier grass (Pennisetum purpureum) in the constructed wetland system. This study has been carried out to investigate the feasibility of the Constructed Wetland in polishing the final discharge according to river quality index. Besides, the propagation of Napier grass in the POME final discharge was evaluated. Four different physicochemical parameters such as chemical oxygen demand (COD), total suspended solid (TSS), ammonia and colour were analysed based on standard laboratory methods and procedures. Results revealed that the reduction of COD level by 71.57 %, TSS by 83.59 %, ammonia by 85.97 % and colour reduced by 87.62 % after 15 days treatment time. In term of propagation of plant, Napier grass showed an excellent propagation in POME final discharge by 13.94% increment. The overall results indicated that treatment of POME final discharge by using Napier grass constructed wetland was successful to reduce the concentration of the contaminants.

Performance Study of Dragon Fruit Foliage as a Plant-based Coagulant for Treatment of Palm Oil Mill Effluent from Three-phase Decanters

This study focused on the performance of dragon fruit foliage as a natural, plant-based coagulant to replace chemical coagulants for the treatment of three-phase decanter palm oil mill effluent (POME). Palm oil mill effluent is a high strength wastewater with high chemical oxygen demand (COD), suspended solids (SS), and turbidity as compared to other sources of POME in mills. The first objective of this study was to determine the optimum operating conditions of the coagulation-flocculation process using the plant-based coagulant in terms of pH and dosage. The second objective was to measure the percentage removal of COD, SS, and turbidity using the coagulant to treat the POME. The pH values and dosages used in the coagulation-flocculation process were in the range of two to ten and 300 mg/L to 800 mg/L, respectively. This study revealed that the optimum percentage removals of COD, SS, and turbidity were 48.7%, 98.8%, and 99.2%, respectively, at the best operating conditions of pH 2 and a coagulant dosage of 300 mg/L. In conclusion, the dragon fruit foliage, plant-based coagulant was found to have potential and could be used in the pretreatment stages to substitute chemical coagulants for the treatment of POME.

Microwave enhanced advanced oxidation treatment of municipal wastewater sludge

Three sludge types (primary sludge, secondary sludge, and anaerobic digested sludge) and centrate produced from a local municipal wastewater treatment plant were treated by the microwave enhanced advanced oxidation process. All sludge types exhibited a certain degree of solids solubilization and phosphorus release, as well as altered physical properties after the treatment. The extent of treatment was influenced by the inherent characteristics of sludge itself, besides the treatment process conditions, such as temperature and hydrogen peroxide dosage. The microwave enhanced advanced oxidation process was very effective for the treatment of all types of sludge for purpose of solids solubilisation, and nutrients release for resource recovery. Very high soluble chemical oxygen demand concentrations (62%) and total suspended solids reduction (75%) were obtained in the treated secondary sludge conducted in the pilot-scale continuous-flow system. The microwave enhanced advanced oxidation treatment system shall be used for treating both primary and secondary sludge, and therefore, the system shall be installed in the treatment train after an aerobic biological treatment system, and before an anaerobic digestion system to gain the maximum process efficiency.

A novel symbiotic system combining algae and sludge membrane bioreactor technology for wastewater treatment and membrane fouling mitigation: Performance and mechanism

A novel Algal-Sludge Bacterial-Membrane bioreactor (ASB-MBR) system, which combined a sludge membrane bioreactor and an algal system in a single tank, was developed in this study. The combined system exhibited excellent wastewater treatment performance, sludge flocs properties and membrane permeability. Compared with conventional MBR (C-MBR), ASB-MBR showed 25% faster growth rate. Meantime, the removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN) and phosphate (PO43−-P) in ASB-MBR were increased by 4.6%, 6.7%, 10.1% and 8.2%, respectively. Amelioration of microbial activity and the increase of dissolved oxygen (DO) concentration were identified as the main reasons for better COD and nitrogen removal, while algal great assimilation and “luxury” uptake of phosphorus and high mixed liquor suspended solids (MLSS) removal contributed to higher PO43−-P removal in ASB-MBR. Moreover, the membrane fouling was mitigated by 50% after inoculating algae. Further mechanism investigation demonstrated that algae has a positive influence on the inhibition of the filamentous bacteria overgrowth and the decrease of zeta potential absolute value, thus improved the flocs flocculability and stability in ASB-MBR. ASB-MBR exhibited higher SMPpr/SMPps ratio, lower bound extracellular polymeric substances (bound EPS) concentrations and smaller Pr/Ps ratio in bound EPS, which contributed to improve the flocs filterability and decrease the fouling layer accumulation. Deposited by this modified sludge, the flocs morphology of the bio-cake in ASB-MBR was more regular and less easy to accumulate on membrane surface resulted in higher membrane permeability.

Profitable ultrasonic assisted microwave disintegration of sludge biomass: Modelling of biomethanation and energy parameter analysis

In this study, microwave irradiation has been employed to disintegrate the sludge biomass profitably by deagglomerating the sludge using a mechanical device, ultrasonicator. The outcomes of the study revealed that a specific energy input of 3.5 kJ/kg TS was found to be optimum for deagglomeration with limited cell lysis. A higher suspended solids (SS) reduction and biomass lysis efficiency of about 22.5% and 33.2% was achieved through ultrasonic assisted microwave disintegration (UMWD) when compared to microwave disintegration – MWD (15% and 20.9%). The results of biochemical methane potential (BMP) test were used to estimate biodegradability of samples. Among the samples subjected to BMP, UMWD showed better amenability towards anaerobic digestion with higher methane production potential of 0.3 L/g COD representing enhanced liquefaction potential of disaggregated sludge biomass. Economic analysis of the proposed method of sludge biomass pretreatment showed a net profit of 2.67 USD/Ton respectively.

Effects of high-concentration influent suspended solids on aerobic granulation in pilot-scale sequencing batch reactors treating real domestic wastewater

The aim of this study was to investigate the effect of high-influent-concentration suspended solids (SS) on the cultivation, structure and long-term stability of aerobic granular sludge (AGS). Cultivation and long-term stability of AGS were monitored in two pilot-scale sequencing batch reactors fed with raw (R1) and settled (R2) domestic wastewater, representing high and medium SS content, respectively. The real domestic wastewater had high chemical oxygen demand (COD) content (1100 ± 270 mg COD L−1). Aerobic granular sludge was cultivated in 44 days (R1) and 25 days (R2) under the conditions of high settling velocity (18 m h−1) and high organic loading rate (OLR) (2.1–2.4 kg COD m3 day). The AGS in both reactors had similar structural properties during long-term operation and remained structurally and functionally stable during the last five months of operation. Comparative evaluation of the results indicated that the high influent SS content of the real domestic wastewater had a positive influence on maintaining significantly lower SVI30 and relatively lower effluent SS concentration. Moreover, a higher influent SS content resulted in smaller mature granules during the stable period. Microbial community analyses helped to understand the aerobic granular sludge structure and showed that the sludge retention time and OLR affected the granular sludge population. The high influent SS increased biomass detachment from the granular sludge surface and caused wash-out of some bacteria colonizing the exterior of the granular sludge.

Physico–chemical Characteristics and Dewatering Aptitude of sMBR Sludge

Biomass concentrations 2 to 5 times higher than in a conventional activated sludge (CAS) process can be achieved in a membrane bioreactor system (MBR). These non–conventional operating conditions, i.e. high sludge concentration, can induce different sludge characteristics and dewatering aptitude, essential parameters for the optimization of the sludge post–treatment, like mechanical dewatering. The objective of this work is to study the dewatering behavior of MBR sludge, and particularly the influence of high total suspended solids concentration, on viscosity and on the key dewaterability indicators. Operating conditions are chosen to obtain MBR sludge with constant characteristics, except TSS concentration. The results confirm that the sludge viscosity is dependent on the TSS concentration. The high viscosity obtained for high TSS concentration can be unfavorable to an efficient mixing in the MBR unit, as well as to acceptable membrane permeability. However, good settleability is obtained with high TSS concentration although the sludge presents high compressibility property and a large part of bound water. This large part of bound water seems to not disturb the sludge filterability, which stays relatively good in comparison with CAS. Consequently, high–TSS concentration in MBR system can be coherent with an efficient sludge post–treatment.

Migration of two antibiotics during resuspension under simulated wind–wave disturbances in a water–sediment system

In this study, the migration of antibiotics (norfloxacin, NOR; and sulfamethoxazole, SMX) under simulated resuspension conditions across the sediment-water interface were quantified for two locations in China: point A, located in Meiliang Bay of Lake Taihu, and point B, located in Dapukou of Lake Taihu. The concentrations of suspended solids (SS) in the overlying water amounted to 100, 500, and 1000 mg/L during background, moderate, and strong simulated wind–wave disturbances, respectively. At each SS level, the initial concentrations of the two antibiotics were set to 1, 5, and 10 mg/L. The results showed that both resuspended SS and the initial concentration of antibiotics could influence the migration of NOR in the water–sediment system. Specifically, both higher SS and initial antibiotic concentrations were associated with higher rates of migration and accumulation of NOR from water to sediment. In contrast, the migration of SMX in the water–sediment system was not impacted by SS or initial antibiotic concentration. The adsorption capacities of sediments for NOR and SMX were significantly different at both locations, possibly reflecting differences in cation exchange capacity (CEC) and organic material (OM) contents. In general, higher CEC and OM values were found in sediments with a higher adsorption capacity for the antibiotics. When CEC and OM values of sediments were higher, the adsorption capacity reached up to 51.73 mg/kg. Large differences in the migration from water to sediment were observed for the two antibiotics, with NOR migration rates higher than those of SMX. The accumulation of NOR in surface sediment during resuspension was about 14 times higher than that of SMX. The main reason for this is that the chemical adsorption of NOR is seldom reversible. Overall, this study demonstrates that resuspension of NOR and SMX attached to sediments under simulated wind–wave disturbances can promote the migration of the antibiotics from water to sediment; these results could be useful for assessing the migration and fate of commonly used antibiotics in water–sediment systems.

Optimization of Operation and Backwashing Condition for an Upflow Stormwater Filtration System Utilizing Ceramic Media

Stormwater filtration is widely used for the urban runoff treatment. However, intensive maintenance and lack of information about the performance have resulted in an increased need of proper evaluation. In this study, the performance of an upflow stormwater runoff filtration system, consisting of a supporting unit and a filtration unit filled with a ceramic media, was investigated. The maximum head loss increase was about 3 cm under the suspended solid (SS) load of 30 kg/m2 and the SS removal was more than 96%, when the filtration velocity was 20-40 m/h. The head loss and the porosity of the media can successfully be described by a power model. It was confirmed that the a significant amount of SS can effectively be removed at supporting unit, minimizing SS load to the filter media bed. Several backwashing strategies have been tested to establish the optimum condition. It was found that the stagnant water discharge is important to minimize the SS release immediately after backwashing. Also, the filter bed loaded with 400-450 kg/m2 SS can almost completely be washed to reduce the head loss to the that of empty bed. The results in this study indicate that the upflow ceramic media filter is an excellent alternative to stormwater treatment, with high SS removal and long lifespan. Key words: Non-Point Source Pollution, Stormwater Runoff, Upflow Filtration System, Backwash

Effects of local land-use on riparian vegetation, water quality, and the functional organization of macroinvertebrate assemblages

Land-use change is a principal factor affecting riparian vegetation and river biodiversity. In Chile, land-use change has drastically intensified over the last decade, with native forests converted to exotic forest plantations and agricultural land. However, the effects thereof on aquatic ecosystems are not well understood. Closing this knowledge gap first requires understanding how human perturbations affect riparian and stream biota. Identified biological indicators could then be applied to determine the health of fluvial ecosystems. Therefore, this study investigated the effects of land-use change on the health of riparian and aquatic ecosystems by assessing riparian vegetation, water quality, benthic macroinvertebrate assemblages, and functional feeding groups. Twenty-one sites in catchment areas with different land-uses (i.e. pristine forests, native forests, exotic forest plantations, and agricultural land) were selected and sampled during the 2010 to 2012 dry seasons. Riparian vegetation quality was highest in pristine forests. Per the modified Macroinvertebrate Family Biotic Index for Chilean species, the best conditions existed in native forests and the worst in agricultural catchments. Water quality and macroinvertebrate assemblages significantly varied across land-use areas, with forest plantations and agricultural land having high nutrient concentrations, conductivity, suspended solids, and apparent color. Macroinvertebrate assemblage diversity was lowest for agricultural and exotic forest plantation catchments, with notable non-insect representation. Collector-gatherers were the most abundant functional feeding group, suggesting importance independent of land-use. Land-use areas showed no significant differences in functional feeding groups. In conclusion, anthropogenic land-use changes were detectable through riparian quality, water quality, and macroinvertebrate assemblages, but not through functional feeding groups. These data, particularly the riparian vegetation and macroinvertebrate assemblage parameters, could be applied towards the conservation and management of riparian ecosystems through land-use change studies.

Treatment of highly toxic cardboard plant wastewater by a combination of electrocoagulation and electrooxidation processes

The objective of this study was to investigate the removal efficiencies of the electrochemical treatment systems as an alternative for the treatment of cardboard plant wastewater (CPW). In accordance with this purpose, CPW was treated by electrocoagulation (EC) with Al electrodes and the effects of current density (CD), operating time (t), and initial pH (pHi) were investigated. The results showed that EC at optimum treatment conditions (CD: 7.5mA/cm2, pHi: 7.0 and t: 60min) have limited removal efficiencies for total organic carbon (TOC; 17.1%) and chemical oxygen demand (COD, 14.2%), on the contrary of turbidity (98.7%). Due to the low TOC and COD removal efficiencies, a secondary treatment was needed and the electrocoagulated effluent was subjected to electrooxidation (EO) by using a boron doped diamond (BDD) electrode for investigating the effect of CD, t, pHi and electrolyte concentration (Ce). Higher TOC (83.7%) and COD (82.9%) removal efficiencies were obtained by EO under the optimum treatment conditions (CD: 100mA/cm2, pHi: 7.2, Ce: 5.0g/L Na2SO4 and t: 180min). In addition, a toxicity test was carried out to the raw and treated wastewater under the optimum operating conditions. This study demonstrated that the combination of EC and EO have a satisfactory potential for real industrial wastewater with a high organic content, suspended solids and toxicity.

Fish-mediated changes in bacterioplankton community composition: an in situ mesocosm experiment

We characterized variations in bacterioplankton community composition (BCC) in mesocosms subject to three different treatments. Two groups contained fish (group one: Cyprinus carpio; group two: Hypophthalmichthys molitrix); and group three, the untreated mesocosm, was the control. Samples were taken seven times over a 49-d period, and BCC was analyzed by PCR-denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR (qPCR). Results revealed that introduction of C. carpio and H. molitrix had a remarkable impact on the composition of bacterioplankton communities, and the BCC was significantly different between each treatment. Sequencing of DGGE bands revealed that the bacterioplankton community in the different treatment groups was consistent at a taxonomic level, but differed in its abundance. H. molitrix promoted the richness of Alphaproteobacteria and Actinobacteria, while more bands affiliated to Cyanobacteria were detected in C. carpio mesocosms. The redundancy analysis (RDA) result demonstrated that the BCC was closely related to the bottom-up (total phosphorus, chlorophyll a, phytoplankton biomass) and top-down forces (biomass of copepods and cladocera) in C. carpio and control mesocosms, respectively. We found no evidence for top-down regulation of BCC by zooplankton in H. molitrix mesocosms, while grazing by protozoa (heterotrophic nanoflagellates, ciliates) became the major way to regulate BCC. Total bacterioplankton abundances were significantly higher in C. carpio mesocosms because of high nutrient concentration and suspended solids. Our study provided insights into the relationship between fish and bacterioplankton at species level, leading to a deep understanding of the function of the microbial loop and the aquatic ecosystem.

Swine manure treatment by anaerobic membrane bioreactor with carbon, nitrogen and phosphorus recovery.

Swine manure wastewater was treated in an anaerobic membrane bioreactor (AnMBR) that combined a continuous stirred tank reactor (CSTR) and a hollow-fiber ultrafiltration membrane, and the feasibility of ammonia and phosphorus recovery in the permeate was investigated. The AnMBR system was operated steadily with a high mixed liquor suspended solids (MLSS) concentration of 32.32 ± 6.24 g/L for 120 days, achieving an average methane yield of 280 mL/gVSadded and total chemical oxygen demand removal efficiency of 96%. The methane yield of the AnMBR is 83% higher than that of the single CSTR. The membrane fouling mechanism was examined, and MLSS and the polysaccharide contents of the extracellular polymeric substances were found to be the direct causes of membrane fouling. The effects of the permeation/relaxation rate and physical, chemical cleaning on membrane fouling were assessed for membrane fouling control, and results showed that a decrease in the permeation/relaxation rate together with chemical cleaning effectively reduced membrane fouling. In addition, a crystallization process was used for ammonia and phosphorus recovery from the permeate, and pH 9 was the optimal condition for struvite formation. The study has an instructive significance to the industrial applications of AnMBRs in treating high strength wastewater with nutrient recovery.

Impact of land uses on heavy metal distribution in the Selenga River system in Mongolia

The Selenga River contributes to 50% of the total inflow to Lake Baikal. Large tracts of the Selenga River Basin have been developed for industry, urbanization, mining, and agriculture, resulting in the release of suspended solids (SS) that affect downstream water quality and primary productivity. This study addressed SS as the main factor controlling pollutant transport and the primary indicator of land degradation in the Selenga River system. Tributaries with larger areas dedicated to agricultural use had higher SS concentrations, reaching 862 mg L−1, especially during the high runoff and intensive cultivation season. Although the large SS flux was detected in the main river, the small tributaries were distinguished by high SS concentrations. The high SS concentration corresponded to widespread development in the watershed. Watersheds with high potential of SS release are sensitive to intensive land uses. SS in the river system had a constant elemental composition consisting mainly of Fe and Al oxides, indicating that surface soils were major constituents of the tributary SS. Three minor heavy metals (Zn, Cu, and Cr) appeared in high concentrations downstream of urban and mining areas (two- to sixfold increases), indicating that these contaminants are carried by SS. At two tributary junctions, the concentration of contaminants on the SS decreased due to a large influx of SS with low heavy metal contents. Changes in electric conductivity and pH at downstream of tributary junctions enhanced the sedimentation of SS and the removal of contaminants from the water phase after aggregation of the SS. Land use changes in the tributary watersheds are major controlling factors for the fate of contaminants in the river system.

Assessment of the Water Quality of Batang Rajang at Pelagus Area, Sarawak, Malaysia

This study was carried out to examine the water quality of Batang Rajang at Pelagus area, Sarawak, Malaysia. Water quality was determined at 12 stations along Batang Rajang and its tributaries in terms of in-situ and ex-situ water quality parameters. The results showed that most stations at main river were categorized as slightly polluted while most tributaries were clean according to the Water Quality Index. The river is suffering from organic pollution where almost all stations along the river contained high chemical oxygen demand (≈ 43.1 mg/L) and total ammonia nitrogen (≈ 0.520 mg/L) and were classified as Class III and IV at most of the stations. High suspended solids (218.3 mg/L) and low dissolved oxygen (4.6 mg/L) were observed at the main river. The low dissolved oxygen content from the Bakun dam upstream of the study area has an impact on the river particularly during dry season where DO dropped below the minimum required for sensitive aquatic organisms. As seven tributaries are within Class II indicating healthy freshwater ecosystems, they should be conserved as habitats for sensitive aquatic organisms. Conversely, proper management need to be initiated in particular, Sungai Merit tributary and the main river where DO were below the minimum required for sensitive aquatic organisms.

Partial nitritation of stored source-separated urine by granular activated sludge in a sequencing batch reactor

The combination of partial nitritation (PN) and anaerobic ammonium oxidation (anammox) has been proposed as an ideal process for nitrogen removal from source-separated urine, while the high organic matters in urine cause instability of single-stage PN-anammox process. This study aims to remove the organic matters and partially nitrify the nitrogen in urine, producing an ammonium/nitrite solution suitable for anammox. The organic matters in stored urine were used as the electron donors to achieve 40% total nitrogen removal in nitritation-denitrification process in a sequencing batch reactor (SBR). Granular aggregates were observed and high mixed liquor suspended solids (9.5 g/L) were maintained in the SBR. Around 70–75% ammonium was oxidized to nitrite under the volumetric loading rates of 3.23 kg chemical oxygen demand (COD)/(m3 d) and 1.86 kg N/(m3 d), respectively. The SBR produced an ammonium/nitrite solution free of biodegradable organic matters, with a NO2−–N:NH4+–N of 1.24 ± 0.13. Fluorescence in situ hybridization images showed that Nitrosomonas-like ammonium-oxidizing bacteria, accounting for 7.2% of total bacteria, located in the outer layer (25 μm), while heterotrophs distributed homogeneously throughout the granular aggregates. High concentrations of free ammonia and nitrous acids in the reactor severely inhibited the growth of nitrite-oxidizing bacteria, resulting in their absence in the granular sludge. The microbial diversity analysis indicated Proteobacteria was the predominant phylum, in which Pseudomonas was the most abundant genus.

Identifying and quantifying environmental thresholds for ecological shifts in a large semi-regulated river

ABSTRACTEcological shifts, between a clear macrophyte-dominated state and a turbid state dominated by phytoplankton and high inorganic suspended solids, have been well described in shallow lake ecosystems. While few documented examples exist in rivers, models predict regime shifts, especially in regulated rivers with high water retention time. Here I quantified ecological shifts in a large, semi-regulated floodplain river during a transition from a turbid- to a clear-water state using water quality, aquatic vegetation and fisheries data from a rigorous, standardized long-term data set. My findings indicate that significant changes occurred in total suspended solids concentration, aquatic macrophyte abundance, native and non-native fish biomass, fish functional feeding guild patterns, fish habitat guild assemblages and fish spawning guild assemblage patterns over a nearly 20-year period in Navigation Pool 8 of the Upper Mississippi River. Transitions in physical and biological indicators were examined to identify mechanisms underlying the ecological shifts. Environmental variables driving fish assemblage changes were identified (total suspended solids and aquatic vegetation) and management-relevant thresholds are presented. Awareness of management thresholds is critical for resource managers to implement measures to prevent the river from moving to a degraded state characterized by high non-native fish abundance and low predatory fish species abundance.

Effect of mean cell residence time on transmembrane flux, mixed-liquor characteristics and overall performance of a submerged anaerobic membrane bioreactor

ABSTRACTKinetic control of Mean Cell Residence Time (MCRT) was shown to have a significant impact on membrane flux under steady-state conditions. Two laboratory-scale flat-plate submerged anaerobic membrane bioreactors were operated for 245 days on a low-to-intermediate strength substrate with high suspended solids. Transmembrane pressure was maintained at 2.2 kPa throughout four experimental phases, while MCRT in one reactor was progressively reduced. This allowed very accurate measurement of sustainable membrane flux rates at different MCRTs, and hence the degree of membrane fouling. Performance data were gathered on chemical oxygen demand (COD) removal efficiency, and a COD mass balance was constructed accounting for carbon converted into new biomass and that lost in the effluent as dissolved methane. Measurements of growth yield at each MCRT were made, with physical characterisation of each mixed liquor based on capillary suction time. The results showed membrane flux and MLSS filterability was highest at short MCRT, although specific methane production (SMP) was lower since a proportion of COD removal was accounted for by higher biomass yield. There was no advantage in operating at an MCRT <25 days. When considering the most suitable MCRT there is thus a trade-off between membrane performance, SMP and waste sludge yield.

Anaerobic digestion of sludge differing in inorganic solids content: performance comparison and the effect of inorganic suspended solids content on degradation.

High inorganic suspended solids (ISS) content of sludge in many areas (especially with combined sewage systems) results in low VS/TS (volatile solids, VS; total solids, TS) levels and raises concerns about its effect on anaerobic digestion. The performances of sludge anaerobic digestion with different feeding VS/TS levels as well as the effect of ISS content on the anaerobic degradation process were investigated in completely stirred tank reactors by semi-continuous and batch experiments. In semi-continuous experiment with sludge at VS/TS of 61.4%, 45.0, 30.0% and 15.0%, biogas yield, VS reduction and methane content decreased logarithmically with the feeding VS/TS decreasing; slightly higher volatile fatty acid concentration was observed at VS/TS 15%. Results of the batch experiments suggested that acetogenesis and methanogenesis are obviously affected by high ISS addition, while hydrolysis is less affected. The retardment of substrate conversion rate is probably attributed to decreased mass transfer efficiency at high ISS content.