Lower Total Ammonia Nitrogen Research Articles

Bioponic Cultivation Using Chicken Droppings to Produce Lettuce Plants (Lactuca sativa rz) Uncontaminated by Trace Metals

Anthropogenic activities have denatured aquatic, terrestrial, and aerial environments throughout the world in general, and in Lubumbashi in particular, where market garden soils have become uncultivable for many plants. Thus, bioponics could be an effective means of producing uncontaminated vegetables in soilless cultivation, not only reducing the amount of fertilizer used and limiting contamination of agricultural produce but also achieving higher yields than in open-ground cultivation. The overall objective of this study was to implement a new bioponic technique for producing liquid fertilizer from chicken manure and utilize it in the organic hydroponic cultivation of lettuce (Lactuca sativa var. Lucrecia) installed on floating raft systems. To achieve this, two types of trials were conducted. The first was aimed at determining the quantities of organic matter to be used in the formulation of nutrient solutions. The second trial aimed to determine the optimal nitrogen concentration to be provided for hydroponic plant growth. Mineralization and/or anaerobic digestion of chicken manure were conducted for 7 days in 200 L barrels. For the first trial, nutrient solutions were created from three different concentrations of chicken manure (0.35%, 3.5%, and 7% dry matter—D.M.). These solutions were then used in bioponic rafts where total ammonia nitrogen (TAN) concentrations were fixed at 150 mg/L. For the second trial, D.M. was fixed at 2.5% for each tested modality, but TAN concentrations varied among them (i.e., 60, 90, and 120 mg/L TAN concentration). Modalities with low D.M. concentration (0.35%) and those with low TAN concentration (60 mg/L) resulted in higher yields than bioponic modalities receiving high concentrations of dry matter or TAN, respectively, for trials 1 and 2. Although the reference chemical solutions generate the greatest yields, bioponic systems operating with chicken manure present a good alternative for the cultivation of vegetables in developing countries with heavily contaminated soils. Indeed, bioponics allows for the production of vegetables in large quantities from animal waste, which does not pose health risks for human consumption. Local vegetable species commonly grown in Lubumbashi should be tested under hydroponic conditions.

Feeding management and appraisal of recirculating aquaculture system for spiny lobster Panulirus spp. weaning

The study aimed to assess lobster fry adaptation to a formulated diet over 1-3 days while evaluating the recirculating system's performance. 1,500 pueruli lobsters (average weight: 0.31 ± 0.01 g) were placed in 30 round 80 L tanks for 30 days. Lobsters underwent various feeding strategies: formulated diet only (FD), adjusting 10% fresh diet per day (D1), every 2 days (D2), every 3 days (D3), and fresh diet only (Fr). Each treatment had five replicates. Results showed feeding strategies influenced lobster growth, with survival rates between 23%-29%. The recommended strategy was adjusting 10% fresh diet every three days, yielding the best performance in final weight (0.93 g), weight gain (187%), and specific growth rate (3.5% per day). Initial weeks saw high mortality and moulting during the puerulus to post-puerulus transition. Water quality analysis indicated the phytobiological filter had lower total ammonia nitrogen (TAN), nitrite-N, nitrate-N, and higher pH compared to other filters in use.

Microbiome analysis reveals microecological advantages of emerging ditchless rice-crayfish co-culture mode

Ditchless rice-crayfish co-culture is an emerging model of rice-crayfish farming that circumvents the potential hazards of digging ditches in traditional rice-crayfish farming. However, due to the complex interactions among crayfish, ambient microbiota, and environmental variables, it is necessary to assess the differences in bacterial structure between ditchless and traditional rice-crayfish culture. In this study, the crayfish culture area in the Sichuan basin was selected as the study area, and the bacterial communities of two rice-crayfish culture systems were compared by high-throughput sequencing of 16S rDNA. The results showed that the ditchless system had lower water depth, higher dissolved oxygen, lower total ammonia nitrogen and lower morbidity. There are intuitive differences in the composition of environmental bacterial communities due to environmental changes, even if they are similar in composition at the phylum level. Microbiota in sediments from ditchless systems appear to produce less ammonia nitrogen. The abundance of the pathogens colonizing the intestine of ditchless crayfish was lower than ditched one, and the composition was similar to water. Ditch-farmed crayfish appear to be more susceptible to environmental microbes and have a more fragile intestinal structure. Water depth and dissolved oxygen are the main environmental factors that determine the distribution of microbiota. This study is the first to investigate the bacterial ecology of a ditchless rice- crayfish farming system. The results show that the ditchless rice-crayfish culture model has a more superior bacterial system than the traditional rice-crayfish culture.

Evaluation of Salipiger thiooxidans and Exiguobacterium aestuarii from the Saemangeum Reservoir as Potential Probiotics for Pacific White Shrimp (Litopenaeus vannamei).

In this study, two bacterial species, Salipiger thiooxidans and Exiguobacterium aestuarii, were extracted and screened from the Saemangeum Reservoir. This study examined these species’ suitability as a probiotic by confirming the effects of S. thiooxidans and E. aestuarii added to rearing water for L. vannamei. Three experimental groups were evaluated for 6 weeks: (1) a control group reared in natural (i.e., untreated) water (CON), (2) an experimental group in which S. thiooxidans was added to natural water (SMG-A), and (3) natural water inoculated with E. aestuarii (SMG-B). The SMG-B group inoculated with E. aestuarii showed significantly higher final body weight, weight gain, specific growth rates, and feed efficiency than the control group. The SMG-B group inoculated with E. aestuarii exhibited significantly higher levels of serum lysozyme, and ACP and ALP activity than the control and SMG-A groups. The SMG-A and SMG-B groups inoculated with probiotics showed significantly lower total ammonia nitrogen and nitrite than the control group. Our findings suggest that S. thiooxidans and E. aestuarii extracted from the Saemangeum Reservoir can improve the water quality of aquaculture water, and, in particular, E. aestuarii is a potential probiotic for L. vannamei.

Primary sludge-based blackwater favors electrical current over methane production in microbial electrochemical cells

Microbial electrochemical cells (MXCs) represent a technology that could potentially be used for decentralized blackwater treatment and resource recovery in remote locations, such as space. One challenge for blackwater treatment in MXCs is achieving sufficient conversion of complex organics to electrical current, especially by preventing electron diversion to dead-end products, such as methane. In this study, we evaluated the effect of source separation (treating feces and urine separately versus combined) on electron diversion to methane in MXCs. We operated five microbial electrolysis cells (MECs) in batch mode, two treating a synthetic primary sludge-based blackwater (PS-BW) with total ammonia nitrogen (TAN) concentration of 475 mg N/L representing combined blackwater (urine and feces), two treating PS-BW with a TAN concentration of 40 mg N/L representing a source separated blackwater (feces only), and one control fed only inoculum, which was anaerobic digester sludge. Chemical oxygen demand (COD) conversion to electrical current in the low and high TAN PS-BW fed MXC was 22% and 21%, respectively, while 1% or less was to methane. Biochemical methane potential assays demonstrated possible methane production from the PS-BW fed to the MXCs. Dysgonomonadaceae and Rikenellaceae dominated the suspension microbial communities of PS-BW fed MECs compared to the inoculum. Bacteria belonging to family Geobacteraceae, known anode-respiring bacteria, dominated the biofilms. Overall, PS-BW, whether combined or source-separated, appeared to limit electron diversion to undesirable methane likely due to the complexity of the PS-BW and the pre-establishment of a robust anode biofilm.

Quillaja saponaria and/or linseed oil improved growth performance, water quality, welfare profile and immune‐oxidative status of Nile tilapia, Oreochromis niloticus fingerlings

This study was aimed to evaluate the synergistic effect of Quillaja Saponaria (QS) and linseed oil (LO) on water quality, growth performance, welfare profile, blood health and immune-oxidative status of Nile tilapia, Oreochromis niloticus fingerlings. Fish (n = 120, 10.28 ± 0.521 g) were randomly distributed in 12 aquaria in triplicate. Fish were divided into four groups: (1) fish received only basal diet (control group, CG), (2) basal diet supplemented with 300 mg kg−1 Quillaja Saponaria (QS), (3) basal diet supplemented with 2% linseed oil (LO) and (4) basal diet supplemented with 300 mg kg−1 Quillaja Saponaria and 2% linseed oil (QS/LO). Results revealed a significant (p < 0.05) improvement in fish productivity (final weight, weight gain, specific growth rate and feed conversion ratio), water quality (low total ammonia nitrogen and unionized ammonia) and welfare indices (low detached scales and fin damage) in fish received QS and/or LO with the best findings being detected in QS/LO. Dietary inclusion of QS and/or LO increased the serum total protein and globulin and reduced the cholesterol and triglycerides compared with CG (p < 0.05) with the best findings in QS/LO. Antioxidant enzymes (increased catalase, superoxide dismutase and reduced malonaldehyde), digestive enzymes (lipase and amylase) and relative gene expression (insulin growth factor I, superoxide dismutase, tumour necrosis factor-alpha) were improved when fish received QS and/or LO with the best results in QS/LO. In conclusion, dietary supplementation of QS and/or LO improved growth performance, water quality, welfare profile and immune-oxidative status of Nile tilapia fingerlings. The best findings being reported in fish received QS/LO.

Dynamics of Microbial Community During Nitrification Biofilter Acclimation with Low and High Ammonia.

The acclimation of a nitrifying biofilter is a crucial and time-consuming task for setting up a recirculating aquaculture system (RAS). Gaining a better understanding of the dynamics of the microbial community during the acclimation period in the system could be useful for the development of mature nitrifying biofilters. In this study, high-throughput DNA sequencing was applied to monitor the microbial communities on a biofilter during the acclimation period (7weeks) in high (100mgN/L) and low (5mgN/L) total ammonia nitrogen (TAN) treatments. Both treatments were successful for developing a mature nitrifying biofilter, dominated by Proteobacteria, Bacteroidetes, and Nitrospirae. Complete nitrification was found after 7days of biofilter acclimation as indicated by decreasing TAN concentration, increasing nitrate concentration, and high abundances of the nitrifying bacteria, Nitrosomonadaceae and Nitrospiraceae. The beta diversity analysis of microbial communities showed different clustering of the samples between high and low TAN treatment groups. A greater abundance of nitrifying bacteria was found in the high TAN treatments (27-51%) than in the low TAN treatment (15-29%). The bacterial diversity in biofilters acclimated at high TAN concentration (Shannon's index 5.40-6.15) were lower than those found at low TAN treatment levels (Shannon's index 6.40-7.01). The higher diversity in biofilters acclimated at low TAN concentrations, consisting of Planctomycetes and Archaea, might benefit the nutrient recycling in the system. Although nitrification activity was observed from the first week of the acclimation period, the acclimation period should be taken as at least 6weeks for full development of nitrifying biofilm. Moreover, the reduction of potentially pathogenic Vibrio on biofilters was found at that period.

Impact of low loading on digestion of the mechanically-separated organic fraction of municipal solid waste

Changing waste management practice, introduction of new technologies, and population demographics and behaviour will impact on both quantity and composition of future waste streams. Laboratory-scale anaerobic digestion of the mechanically-separated organic fraction of municipal solid waste (ms-OFMSW) was carried out at relatively low organic loading rates (OLR), and results analysed using an energy modelling tool. Thermophilic operation with water addition and liquor recycle was compared to co-digestion with dilution water replaced by sewage sludge digestate (SSD); thermophilic and mesophilic mono-digestion were also tested at low OLR. All thermophilic conditions showed stable operation, with specific methane production (SMP) from 0.203 to 0.296 m3 CH4 kg−1 volatile solids (VS). SSD addition increased biogas production by ~20% and there was evidence of further hydrolysis and degradation of the SSD. Long-term operation at 1 kg VS m−3 day−1 had no adverse effect except in mesophilic conditions where SMP was lower at 0.256 m3 CH4 kg−1 VS and stability was reduced, especially during OLR increases. This was probably due to low total ammonia nitrogen, which stabilised at ~0.2 g N kg−1 and limited the buffering capacity. Energy analysis showed thermophilic operation at OLR 2 g VS L−1 day−1 gave 42% of the theoretical methane potential and 38% of the higher heating value, reducing to 37% and 34% respectively in mesophilic conditions. Scenario modelling indicated that under low ms-OFMSW load even an energy-depleted co-substrate such as SSD could contribute to the energy balance, and would be a better diluent than water due to its nutrient and buffering capacity.

Organ-specific responses to total ammonia nitrogen stress on juvenile grass carp (Ctenopharyngodon idellus).

Fish are important in constructed wetland (CW) ecosystem. An 80-day experiment was conducted by exposing juvenile grass carp (Ctenopharyngodon idellus) to 0, 0.5, 2.0, 4.5, 9.0, and 18.0mgL-1 total ammonia nitrogen (TAN) stress to determine the severity of physiological changes in fish organs (liver, gills, and muscle) in CW. Specific growth rate results indicated that low TAN (≤ 2.0mgL-1) help maintain or enhance grass carp growth. Fish physiological indexes did not significantly change during exposure, except for the gill's reactive oxygen species (ROS) level that is susceptible to TAN exposure. Under high TAN (≥ 4.5mgL-1), physiological changes and organ-specific responses were revealed. The ROS and malondialdehyde levels were higher in the gills than in the liver. At 9.0mgL-1 TAN, the muscle cells manifested toxicity. The antioxidant system of different organs responded differently because the gills were more susceptible to low TAN than other organs. After TAN removal from the low TAN system, the antioxidative enzymes and antioxidants were increased to scavenge extra ROS and reverted to the normal level. However, grass carp cannot recover from the oxidative damage at ≥ 9.0mgL-1 external TAN, resulting in organ dysfunction and failed ROS scavenging. This study provides information in maintaining CW sustainability.

The effect of low pH on physiology, stress status and growth performance of turbot (Psetta maximaL.) cultured in recirculating aquaculture systems

We evaluated the effect of low pH and low and high total ammonia nitrogen (TAN) concentrations on the physiology, stress status and the growth performance of turbot in RAS. Two experiments were conducted. In Experiment 1, turbot (466 g) were grown at control (pH 7.5; TAN ~0.5 mg/L) or low pH and high TAN (pH 5.7; TAN ~50 mg/L) for 55 days. In Experiment 2, turbot (376 g) were grown at control (pH 7.5; TAN ~0.5 mg/L), low pH and low TAN (pH 5.7; TAN ~5 mg/L) or low pH and high TAN (pH 5.7; TAN ~50 mg/L) for 59 days. In Experiment 1, final body weight, feed intake and growth were significantly lower and FCR significantly higher in turbot exposed to low pH and high TAN. In Experiment 2, only growth was significantly lower in turbot exposed to treatment low pH and high TAN as compared to fish in the control treatment and low pH and low TAN. Osmoregulation and stress indicators measured were within normal levels. In conclusion, turbot grew equally well in a water pH of 7.5 or 5.7 provided a low TAN. In contrast, low pH combined with a high TAN impaired turbot performance.

A combination of ammonia stripping and low temperature thermal pre-treatment improves anaerobic post-digestion of the supernatant from organic fraction of municipal solid waste treatment

Municipal Solid Waste is mostly composed of organic material which is often treated in anaerobic reactors in waste treatment plants. In most cases, the obtained digestate undergoes a solid/liquid separation step, producing a liquid fraction (known as anaerobic supernatant) rich in ammonium nitrogen that has to be further treated in order to meet discharge standards. The objective of the present work was to evaluate the feasibility of anaerobic post-digestion (37 °C) of a supernatant rich in carbon and nitrogen from a municipal waste treatment plant. In order to increase the efficiency of the process, a combined pre-treatment consisting of a low-temperature thermal process (75 °C) and ammonia stripping (1.3 Lair Lsupernatant−1 min−1) was applied. The effects of pre-treatment contact time (4 and 8 h) and the hydraulic retention time (HRT) in the anaerobic reactor (20–40 d) were studied. Supernatant pre-treatment with 8-h contact time caused 13% organic matter solubilisation, thus improving methanisation by 18% when the HRT was 40 d. At the same time, ammonia stripping allowed to maintain ammonia concentration in the digester below inhibitory values (less than 100 mg N-NH3 L−1) enabling therefore high methanogenic activity (>0.23 g COD g−1 VS d−1). The final effluent characteristics (low total ammonia nitrogen and aerobically biodegradable organic matter levels) would permit implementing subsequent less energy intensive and more environmental-friendly technologies (such as partial nitritation/anammox) to comply with discharge limits.

Temperature, density and ammonia effects on growth and fecundity of the ramshorn snail (Helisoma anceps)

Ramshorn snail (Helisoma anceps) is a freshwater gastropod found all over North America and is also an essential component to the larval and juvenile culture of endangered Delta Smelt (Hypomesus transpacificus) at the UC Davis Fish Conservation and Culture Lab (FCCL). H. anceps has been proven effective in cleaning the excess algae while not harming the larvae. A challenge at the FCCL has been having a reliable source of these snails, since previously it has been dependent upon nature and never guaranteed there would be enough to meet the needs of the FCCL. Experiments were conducted to assess the effects of temperature, food types, rearing density and total ammonia nitrogen (TAN) concentrations. Procedures recommended to increase snail fecundity for the FCCL are to rear spawning parent snails and the resultant eggs at a high temperature (16–20°C) and with a low TAN concentration (0–5 mg/L). Newly hatched snails need to be cultured at a low density (about one snail/20 cm2). After the snails grow to an acceptable size (1.3 cm diameter), they could be set aside and cultured in an environment with less optimal water quality parameters such as a high TAN level (as high as 20 mg/L) and low temperature (12°C) for quantity control prior to use.

Mixing and scale affect moving bed biofilm reactor (MBBR) performance

Moving Bed Biofilm Reactors (MBBR) are used increasingly in closed systems for farming of fish. Scaling, i.e. design of units of increasing size, is an important issue in general bio-reactor design since mixing behaviour will differ between small and large scale. Research is mostly performed on small-scale biofilters and the question is to what extent this can be upscaled to a commercial level. Therefore, the objective of this research was to establish the effect of mixing and scale on MBBR performance. The research was done in two major parts; firstly effects of scale-sensitive factors were studied in small reactors. Secondly, performance of these small reactors was then compared to increasingly large reactor sizes, using the same inlet water quality and biofilm.Firstly, a 200L MBBR (medium scale) was operated continuously using a synthetic feed solution. Biofilm carriers from this reactor was used for short-term experiments in 0.8L reactors (small scale) and compared with the performance of the 200L medium scale reactor. Reactor geometry and superficial air velocity (mh−1) were identical in these experiments. Subsequently, the small reactors were incubated with biofilm carriers from three commercial farms and performance compared with these large scale reactors. In a number of additional experiments the effect of mixing and Total Ammonia Nitrogen (TAN) was tested at small and medium scale.The results showed that MBBR scale has a significant effect on TAN removal rate. In general, the larger the scale the better the performance. TAN removal (rTAN) at small scale (0.8L) is about 80% compared to that at medium scale (200L). The difference between small scale and large scale (>20m3) is even higher. These findings warrant further studies on whether a plateau is reached in rTAN at a certain scale; a study which will have considerable importance for optimal design and dimensioning of commercial scale RAS. It was further found that superficial air velocity is not a good scaling factor for MBBRs. Upscaling while maintaining geometry implies increasing air injection depth and therefore increased energy input will be required at a comparable superficial air velocity, which is not incorporated in the superficial air velocity term (mh−1). Superficial air velocity and media filling% were found to have a strong effect on mixing time at small scale. An air velocity below a threshold of 5mh−1 decreased TAN removal at both small and medium scale. Intense mixing at small scale increased TAN removal at low TAN concentration. However, at a high TAN concentration, the small scale MBBR always performed at not more than 80% of the capacity of the medium scale system, irrespective of the mixing conditions. Hence, the capacity of full scale systems will be under-estimated when based solely on small scale experiments.

Mixed-matrix membranes for efficient ammonium removal from wastewaters

Novel mixed matrix membranes and fibers were fabricated to investigate ammonium removal for the first time from wastewaters especially aquaculture wastewaters. Several approaches were adopted to fabricate these mixed-matrix membranes including a wet phase inversion process as well as pore filling of commercially available membranes. Natural zeolite particles were effectively incorporated into polysulfone polymer matrices. These composite materials are found to be efficient for ammonium removal with high capacity and high stability. No leaching of zeolite materials was detected. These mixed-matrix membranes demonstrate high water flux and are easy to regenerate. Over 90% of total ammonia nitrogen (TAN) can be removed from relatively low TAN concentration aquaculture wastewaters. These novel adsorptive membranes are reusable and exhibit high viability for large scale industrial applications.

Deep-sequencing of the bacterial microbiota in commercial-scale recirculating and semi-closed aquaculture systems for Atlantic salmon post-smolt production

New aquaculture production systems are evolving for prolong production of Atlantic salmon smolts or post-smolts before stocking in traditional net pens, such as semi-closed containment systems (S-CCS) in sea (Fig. 1) and recirculating aquaculture systems (RAS) on land. The microbiota in these systems can potentially have great impact on the robustness and health of the fish. These two types of aquaculture systems are likely to have different challenges regarding pathogenic invasion due to the different water management, e.g. different treatment of the intake water and different turnover of the water. In this study, we investigated the bacterial microbiota of both water and biofilms in a commercial RAS and in S-CCS in sea during a three months period of post-smolt production. Deep-sequencing of the bacterial 16S rRNA gene (V4) was used for the first time to obtain in depth compositional analysis of microbial communities in commercial scale facilities. Highly diverse communities were detected, with up to 2000 different Operational Taxonomic Units (OTUs) within samples. Both systems were dominated by Proteobacteria with Rhodobacteraceae as the dominating taxa, followed by Bacteroidetes that was dominated by Polaribacter among others. However, the microbiota composition was clearly different between the two aquaculture systems, and between water samples and biofilms. In RAS, it was also shown different microbiota composition with water salinity of 12 vs 22 parts per thousand (ppt). Higher abundance of e.g. Myxococcales and Nitrospiraceae was observed at 12ppt, which coincided with lower total ammonia nitrogen (TAN) levels. Both taxa were also more abundant in the Moving Bed Bioreactor (MBBR)-biofilms than in water, as well as Planctomyces among others. In S-CCS, clear temporal changes of the microbiota was observed during the production, where potential pathogens like Tenacibaculum, Aliivibrio, Alteromonadaceae and Polaribacter were increasing in the spring time, as well as one unassigned taxa and chloroplast DNA likely from algae. The implication of these potential pathogens on fish health is unknown. A common observation for both RAS and S-CCS was higher abundance of the potential pathogens in the water compared to the biofilms. Further studies on the microbiota in closed-containment aquaculture systems are needed to obtain more knowledge about their impact on post-smolt production performance, welfare and health.

Laboratory tests of bacterial amendments for accelerating oxidation rates of ammonia, nitrite and organic matter in aquaculture pond water

The effects of 12 bacterial amendments on reducing concentrations of total ammonia nitrogen (TAN), nitrite nitrogen (NO2−N) and organic matter in pond waters were evaluated in the laboratory. Concentrations of TAN, NO2−N and organic matter in untreated water (controls) naturally decreased with time during 16days. No large acceleration in nitrification or organic matter oxidation was observed from using these bacterial amendments. However, minor differences in concentrations of TAN and NO2−N, and rates of dissolved oxygen loss – an indicator of decomposition rate – were found between controls and treatments on some sampling dates. Compared to the controls, the bacterial amendment 5 at the manufacturer's recommended dose resulted in lower TAN concentrations on days 8 and 12, less NO2−N on days 6 and 8 and less oxygen loss on day 1. Water treated with the bacterial amendments 3 and 10 at the recommended doses had slightly lower TAN concentrations on day 0 (soon after initial treatment) and day 16, respectively. The bacterial amendment 11 at the recommended dose lead to lower NO2−N concentration on day 12. Organic matter in water treated with the bacterial amendments 8 and 10 exhibited a greater rate of microbial respiration on day 16. With higher doses or more frequent applications, there was lower (P<0.05) TAN concentrations in water treated with the bacterial amendment 11 on day 0 and day 2. The bacterial amendment 10 at higher dose and the bacterial amendment 7 at more frequent applications than recommended by manufacturers had a small effect on oxygen rate loss on day 1 and days 7, 9 and 13, respectively. The bacterial amendments 1, 2, 4, 6, 9 and 12 were not successful (P>0.05) at lowering concentrations of TAN, and NO2−N or oxygen loss rate on any sampling dates. Statement of relevanceBacterial amendments are widely used in aquaculture in efforts to enhance water quality in ponds. This research showed no benefit of bacterial amendments on water quality in laboratory tests and doubts on the effectiveness of bacterial augmentation.

&lt;b&gt;Tolerance of Nile tilapia juveniles to highly acidic rearing water

The present work aimed at determining the tolerance of Nile tilapia juveniles to highly acidic rearing waters and the effects of water acidity on the quality of tank effluents. The experimental design consisted of four treatments with different water pH values (4.12 ± 0.84; 5.13 ± 0.74; 6.14 ± 0.64 and 8.06 ± 0.48), with five replicates each. No exchange of water was performed throughout the study, only water replenishment to maintain the initial level. Variables of water quality, soil, growth performance, metabolism and effluents were monitored for eight weeks. Despite the lower total ammonia nitrogen (TAN) concentration in the pH 8 tanks, their levels of non-ionized ammonia (NH3) were the highest ones. At the end, the lowest body weight of fish was observed in the pH 8 tanks. There was a significant improvement in feed conversion ratio (FCR) and protein efficiency ratio (PER) due to to water acidification. There were reduced concentrations of NH3 in the acidified tanks' effluents. It was concluded that the gradual water acidification up to pH 4 can improve the Nile tilapia juveniles' growth performance.

Effect of ammonia and nitrate on biogas production from food waste via anaerobic digestion

Ammonia accumulation is potentially encountered in anaerobic digestion of food waste, restricting its application in industrial biogas plants. This bench scale study investigated the suitability of nitrification process for ammonia removal from food waste digestate in the recirculated anaerobic digestion system. The effect of ammonia, in terms of total ammonia nitrogen (TAN) on anaerobic digestion of food waste was evaluated over an added concentration range of 0–4.5 g l−1. It was observed that lower TAN concentrations (<1.54 g l−1) were beneficial to anaerobic digestion, while higher TAN concentrations (>3.78 g l−1) caused an excessive inhibition of methanogenesis. In an attempt to simulate conditions of recycling digestate after nitrification treatment into the recirculated anaerobic digestion system, the impact of nitrification products on anaerobic digestion performance was investigated by employing the nitrate as a variable compound with an added TAN concentration of 1.0 g l−1. The results showed that no inhibition of methane production occurred at added NO3–N concentrations below 0.75 g l−1. A maximum methane yield of 314.7 ml g−1 VSadded was obtained at added NO3–N concentration of 0.5 g l−1, which was 11.8% higher than the yield when no nitrate was added. However, methane yield was reduced by 50.8% when added NO3–N concentration exceeded 1.5 g l−1. The results suggest that the nitrification process can be potentially suitable for ammonia removal when the TAN and NO3–N concentrations in the anaerobic reactor after digestate recirculation were less than 1.54 g l−1 and 0.75 g l−1, respectively.

Small crumbled diet versus powdered diet in restricted feeding management of juvenile Nile tilapia

The pellet size of the diet can affect both fish growth performance and the water quality of the rearing units. The present work assessed the effects of feeding juvenile Nile tilapia, Oreochromis niloticus (L.) a small crumbled diet (SCD; 0.8 mm) on water quality and growth performance. Fish were reared for six weeks in twenty 250-L polyethylene outdoor tanks at a density of 10 juveniles tank -1 (40 fish m -3 ). There were two feeding rates (standard and restricted) and two types of artificial fish diet (powdered and SCD). The standard feeding rates were reduced by 30% for restricted feeding. The concentrations of free CO2, reactive phosphorus, total ammonia nitrogen (TAN) and nitrite were higher in the full-fed tanks relative to the restricted-fed tanks. In the standard feeding rate groups, those tanks fed SCD had lower TAN and nitrite concentrations than tanks fed a powdered diet. The final body weight and specific growth rate of fish fed a restricted SCD were higher than the full-fed tanks. The higher levels of food waste in the powdered-diet tanks lead to impairment of fish growth performance.

Interaction between feeding rate and area for periphyton in culture of Nile tilapia juveniles - doi: 10.4025/actascianimsci.v34i2.12469

The objective of the present work was to determine the effects of the interaction between feeding rate and area for periphyton in rearing aquaria for Nile tilapia. Twenty 25 L polyethylene outdoor aquaria were used to hold experimental fish. Three tilapia fingerlings (2.56 ± 0.14 g) were stocked in each aquarium for five weeks (12 fish m-2). There were two different feeding rates (full and full minus 30%) and two submerged areas for periphyton development (59.4% and 96.5% of the aquarium surface area; n = 5). Final body weight, specific growth rate and yield in the 96.5%-area aquaria of fish submitted to 30% less feed were significantly higher than in the 96.5%-area aquaria submitted to full feeding rates. Fish growth in the restricted-feed aquaria was favored by their better water quality (higher pH and lower total ammonia nitrogen). There were negative effects on final body weight, SGR, yield and feed conversion ratio of fish in full-feed aquaria when the area for periphyton increased from 59.4 to 96.5%. It was concluded that the combination of restricted feeding rates with large substrate areas for periphyton growth results in better water quality for fish culture than the adoption of each management alone.